--- rfc2068.txt
+++ rfc2616.txt
@@ -1,14 +1,20 @@
 
 
 Network Working Group                                      R. Fielding
-Request for Comments: 2068                                   UC Irvine
-Category: Standards Track                                    J. Gettys
+Request for Comments: 2616                                   UC Irvine
+Obsoletes: 2068                                              J. Gettys
+Category: Standards Track                                   Compaq/W3C
                                                               J. Mogul
-                                                                   DEC
+                                                                Compaq
                                                             H. Frystyk
+                                                               W3C/MIT
+                                                           L. Masinter
+                                                                 Xerox
+                                                              P. Leach
+                                                             Microsoft
                                                         T. Berners-Lee
-                                                               MIT/LCS
-                                                          January 1997
+                                                               W3C/MIT
+                                                             June 1999
 
                 Hypertext Transfer Protocol -- HTTP/1.1
 
@@ -20,271 +26,285 @@
    Official Protocol Standards" (STD 1) for the standardization state
    and status of this protocol.  Distribution of this memo is unlimited.
 
+Copyright Notice
+
+   Copyright (C) The Internet Society (1999).  All Rights Reserved.
+
 Abstract
 
    The Hypertext Transfer Protocol (HTTP) is an application-level
    protocol for distributed, collaborative, hypermedia information
-   systems. It is a generic, stateless, object-oriented
+   systems. It is a generic, stateless,
-   protocol which can be used for many tasks,
+   protocol which can be used for many tasks beyond its use for hypertext,
such as name servers and distributed object management systems, through extension of its request methods
-   .
+   ,error codes and headers [47].
A feature of HTTP is the typing and negotiation of data representation, allowing systems
to be built independently of the data being transferred.
 
    HTTP has been in use by the World-Wide Web global information
    initiative since 1990. This specification defines the protocol
-   referred to as "HTTP/1.1".
+   referred to as "HTTP/1.1", and is an update to RFC 2068 [33].
 
 Table of Contents
 
-   1 Introduction.............................................7
-    1.1 Purpose ..............................................7
-    1.2 Requirements .........................................7
-    1.3 Terminology ..........................................8
-    1.4 Overall Operation ...................................11
-   2 Notational Conventions and Generic Grammar..............13
-    2.1 Augmented BNF .......................................13
-    2.2 Basic Rules .........................................15
-   3 Protocol Parameters.....................................17
-    3.1 HTTP Version ........................................17
-    3.2 Uniform Resource Identifiers ........................18
-     3.2.1 General Syntax ...................................18
-     3.2.2 http URL .........................................19
-     3.2.3 URI Comparison ...................................20
-    3.3 Date/Time Formats ...................................21
-     3.3.1 Full Date ........................................21
-     3.3.2 Delta Seconds ....................................22
-    3.4 Character Sets ......................................22
-    3.5 Content Codings .....................................23
-    3.6 Transfer Codings ....................................24
-    3.7 Media Types .........................................25
-     3.7.1 Canonicalization and Text Defaults ...............26
-     3.7.2 Multipart Types ..................................27
-    3.8 Product Tokens ......................................28
-    3.9 Quality Values ......................................28
-    3.10 Language Tags ......................................28
-    3.11 Entity Tags ........................................29
-    3.12 Range Units ........................................30
-   4 HTTP Message............................................30
-    4.1 Message Types .......................................30
-    4.2 Message Headers .....................................31
-    4.3 Message Body ........................................32
-    4.4 Message Length ......................................32
-    4.5 General Header Fields ...............................34
-   5 Request.................................................34
-    5.1 Request-Line ........................................34
-     5.1.1 Method ...........................................35
-     5.1.2 Request-URI ......................................35
-    5.2 The Resource Identified by a Request ................37
-    5.3 Request Header Fields ...............................37
-   6 Response................................................38
-    6.1 Status-Line .........................................38
-     6.1.1 Status Code and Reason Phrase ....................39
-    6.2 Response Header Fields ..............................41
-   7 Entity..................................................41
-    7.1 Entity Header Fields ................................41
-    7.2 Entity Body .........................................42
-     7.2.1 Type .............................................42
-     7.2.2 Length ...........................................43
-   8 Connections.............................................43
-    8.1 Persistent Connections ..............................43
-     8.1.1 Purpose ..........................................43
-     8.1.2 Overall Operation ................................44
-     8.1.3 Proxy Servers ....................................45
-     8.1.4 Practical Considerations .........................45
-    8.2 Message Transmission Requirements ...................46
-   9 Method Definitions......................................48
-    9.1 Safe and Idempotent Methods .........................48
-     9.1.1 Safe Methods .....................................48
-     9.1.2 Idempotent Methods ...............................49
-    9.2 OPTIONS .............................................49
-    9.3 GET .................................................50
-    9.4 HEAD ................................................50
-    9.5 POST ................................................51
-    9.6 PUT .................................................52
-    9.7 DELETE ..............................................53
-    9.8 TRACE ...............................................53
-   10 Status Code Definitions................................53
-    10.1 Informational 1xx ..................................54
-     10.1.1 100 Continue ....................................54
-     10.1.2 101 Switching Protocols .........................54
-    10.2 Successful 2xx .....................................54
-     10.2.1 200 OK ..........................................54
-     10.2.2 201 Created .....................................55
-     10.2.3 202 Accepted ....................................55
-     10.2.4 203 Non-Authoritative Information ...............55
-     10.2.5 204 No Content ..................................55
-     10.2.6 205 Reset Content ...............................56
-     10.2.7 206 Partial Content .............................56
-    10.3 Redirection 3xx ....................................56
-     10.3.1 300 Multiple Choices ............................57
-     10.3.2 301 Moved Permanently ...........................57
-     10.3.3 302 Moved Temporarily ...........................58
-     10.3.4 303 See Other ...................................58
-     10.3.5 304 Not Modified ................................58
-     10.3.6 305 Use Proxy ...................................59
-    10.4 Client Error 4xx ...................................59
-     10.4.1 400 Bad Request .................................60
-     10.4.2 401 Unauthorized ................................60
-     10.4.3 402 Payment Required ............................60
-     10.4.4 403 Forbidden ...................................60
-     10.4.5 404 Not Found ...................................60
-     10.4.6 405 Method Not Allowed ..........................61
-     10.4.7 406 Not Acceptable ..............................61
-     10.4.8 407 Proxy Authentication Required ...............61
-     10.4.9 408 Request Timeout .............................62
-     10.4.10 409 Conflict ...................................62
-     10.4.11 410 Gone .......................................62
-     10.4.12 411 Length Required ............................63
-     10.4.13 412 Precondition Failed ........................63
-     10.4.14 413 Request Entity Too Large ...................63
-     10.4.15 414 Request-URI Too Long .......................63
-     10.4.16 415 Unsupported Media Type .....................63
-    10.5 Server Error 5xx ...................................64
-     10.5.1 500 Internal Server Error .......................64
-     10.5.2 501 Not Implemented .............................64
-     10.5.3 502 Bad Gateway .................................64
-     10.5.4 503 Service Unavailable .........................64
-     10.5.5 504 Gateway Timeout .............................64
-     10.5.6 505 HTTP Version Not Supported ..................65
-   11 Access Authentication..................................65
-    11.1 Basic Authentication Scheme ........................66
-    11.2 Digest Authentication Scheme .......................67
-   12 Content Negotiation....................................67
-    12.1 Server-driven Negotiation ..........................68
-    12.2 Agent-driven Negotiation ...........................69
-    12.3 Transparent Negotiation ............................70
-   13 Caching in HTTP........................................70
-     13.1.1 Cache Correctness ...............................72
-     13.1.2 Warnings ........................................73
-     13.1.3 Cache-control Mechanisms ........................74
-     13.1.4 Explicit User Agent Warnings ....................74
-     13.1.5 Exceptions to the Rules and Warnings ............75
-     13.1.6 Client-controlled Behavior ......................75
-    13.2 Expiration Model ...................................75
-     13.2.1 Server-Specified Expiration .....................75
-     13.2.2 Heuristic Expiration ............................76
-     13.2.3 Age Calculations ................................77
-     13.2.4 Expiration Calculations .........................79
-     13.2.5 Disambiguating Expiration Values ................80
-     13.2.6 Disambiguating Multiple Responses ...............80
-    13.3 Validation Model ...................................81
-     13.3.1 Last-modified Dates .............................82
-     13.3.2 Entity Tag Cache Validators .....................82
-     13.3.3 Weak and Strong Validators ......................82
-     13.3.4 Rules for When to Use Entity Tags and Last-
-     modified Dates..........................................85
-     13.3.5 Non-validating Conditionals .....................86
-    13.4 Response Cachability ...............................86
-    13.5 Constructing Responses From Caches .................87
-     13.5.1 End-to-end and Hop-by-hop Headers ...............88
-     13.5.2 Non-modifiable Headers ..........................88
-     13.5.3 Combining Headers ...............................89
-     13.5.4 Combining Byte Ranges ...........................90
-    13.6 Caching Negotiated Responses .......................90
-    13.7 Shared and Non-Shared Caches .......................91
-    13.8 Errors or Incomplete Response Cache Behavior .......91
-    13.9 Side Effects of GET and HEAD .......................92
-    13.10 Invalidation After Updates or Deletions ...........92
-    13.11 Write-Through Mandatory ...........................93
-    13.12 Cache Replacement .................................93
-    13.13 History Lists .....................................93
-   14 Header Field Definitions...............................94
-    14.1 Accept .............................................95
-    14.2 Accept-Charset .....................................97
-    14.3 Accept-Encoding ....................................97
-    14.4 Accept-Language ....................................98
-    14.5 Accept-Ranges ......................................99
-    14.6 Age ................................................99
-    14.7 Allow .............................................100
-    14.8 Authorization .....................................100
-    14.9 Cache-Control .....................................101
-     14.9.1 What is Cachable ...............................103
-     14.9.2 What May be Stored by Caches ...................103
-     14.9.3 Modifications of the Basic Expiration Mechanism 104
-     14.9.4 Cache Revalidation and Reload Controls .........105
-     14.9.5 No-Transform Directive .........................107
-     14.9.6 Cache Control Extensions .......................108
-    14.10 Connection .......................................109
-    14.11 Content-Base .....................................109
-    14.12 Content-Encoding .................................110
-    14.13 Content-Language .................................110
-    14.14 Content-Length ...................................111
-    14.15 Content-Location .................................112
-    14.16 Content-MD5 ......................................113
-    14.17 Content-Range ....................................114
-    14.18 Content-Type .....................................116
-    14.19 Date .............................................116
-    14.20 ETag .............................................117
-    14.21 Expires ..........................................117
-    14.22 From .............................................118
-    14.23 Host .............................................119
-    14.24 If-Modified-Since ................................119
-    14.25 If-Match .........................................121
-    14.26 If-None-Match ....................................122
-    14.27 If-Range .........................................123
-    14.28 If-Unmodified-Since ..............................124
-    14.29 Last-Modified ....................................124
-    14.30 Location .........................................125
-    14.31 Max-Forwards .....................................125
-    14.32 Pragma ...........................................126
-    14.33 Proxy-Authenticate ...............................127
-    14.34 Proxy-Authorization ..............................127
-    14.35 Public ...........................................127
-    14.36 Range ............................................128
-     14.36.1 Byte Ranges ...................................128
-     14.36.2 Range Retrieval Requests ......................130
-    14.37 Referer ..........................................131
-    14.38 Retry-After ......................................131
-    14.39 Server ...........................................132
-    14.40 Transfer-Encoding ................................132
-    14.41 Upgrade ..........................................132
-    14.42 User-Agent .......................................134
-    14.43 Vary .............................................134
-    14.44 Via ..............................................135
-    14.45 Warning ..........................................137
-    14.46 WWW-Authenticate .................................139
-   15 Security Considerations...............................139
-    15.1 Authentication of Clients .........................139
-    15.2 Offering a Choice of Authentication Schemes .......140
-    15.3 Abuse of Server Log Information ...................141
-    15.4 Transfer of Sensitive Information .................141
-    15.5 Attacks Based On File and Path Names ..............142
-    15.6 Personal Information ..............................143
-    15.7 Privacy Issues Connected to Accept Headers ........143
-    15.8 DNS Spoofing ......................................144
-    15.9 Location Headers and Spoofing .....................144
-   16 Acknowledgments.......................................144
-   17 References............................................146
-   18 Authors' Addresses....................................149
-   19 Appendices............................................150
-    19.1 Internet Media Type message/http ..................150
-    19.2 Internet Media Type multipart/byteranges ..........150
-    19.3 Tolerant Applications .............................151
-    19.4 Differences Between HTTP Entities and
-    MIME Entities...........................................152
-     19.4.1 Conversion to Canonical Form ...................152
-     19.4.2 Conversion of Date Formats .....................153
-     19.4.3 Introduction of Content-Encoding ...............153
-     19.4.4 No Content-Transfer-Encoding ...................153
-     19.4.5 HTTP Header Fields in Multipart Body-Parts .....153
-     19.4.6 Introduction of Transfer-Encoding ..............154
-     19.4.7 MIME-Version ...................................154
-    19.5 Changes from HTTP/1.0 .............................154
-     19.5.1 Changes to Simplify Multi-homed Web Servers and
-     Conserve IP Addresses .................................155
-    19.6 Additional Features ...............................156
-     19.6.1 Additional Request Methods .....................156
-     19.6.2 Additional Header Field Definitions ............156
-    19.7 Compatibility with Previous Versions ..............160
-     19.7.1 Compatibility with HTTP/1.0 Persistent
-     Connections............................................161

+   1   Introduction ...................................................7
+   1.1    Purpose......................................................7
+   1.2   Requirements .................................................8
+   1.3   Terminology ..................................................8
+   1.4   Overall Operation ...........................................12
+   2   Notational Conventions and Generic Grammar ....................14
+   2.1   Augmented BNF ...............................................14
+   2.2   Basic Rules .................................................15
+   3   Protocol Parameters ...........................................17
+   3.1   HTTP Version ................................................17
+   3.2   Uniform Resource Identifiers ................................18
+   3.2.1    General Syntax ...........................................19
+   3.2.2    http URL .................................................19
+   3.2.3    URI Comparison ...........................................20
+   3.3   Date/Time Formats ...........................................20
+   3.3.1    Full Date ................................................20
+   3.3.2    Delta Seconds ............................................21
+   3.4   Character Sets ..............................................21
+   3.4.1    Missing Charset ..........................................22
+   3.5   Content Codings .............................................23
+   3.6   Transfer Codings ............................................24
+   3.6.1    Chunked Transfer Coding ..................................25
+   3.7   Media Types .................................................26
+   3.7.1    Canonicalization and Text Defaults .......................27
+   3.7.2    Multipart Types ..........................................27
+   3.8   Product Tokens ..............................................28
+   3.9   Quality Values ..............................................29
+   3.10  Language Tags ...............................................29
+   3.11  Entity Tags .................................................30
+   3.12  Range Units .................................................30
+   4   HTTP Message ..................................................31
+   4.1   Message Types ...............................................31
+   4.2   Message Headers .............................................31
+   4.3   Message Body ................................................32
+   4.4   Message Length ..............................................33
+   4.5   General Header Fields .......................................34
+   5   Request .......................................................35
+   5.1   Request-Line ................................................35
+   5.1.1    Method ...................................................36
+   5.1.2    Request-URI ..............................................36
+   5.2   The Resource Identified by a Request ........................38
+   5.3   Request Header Fields .......................................38
+   6   Response ......................................................39
+   6.1   Status-Line .................................................39
+   6.1.1    Status Code and Reason Phrase ............................39
+   6.2   Response Header Fields ......................................41
+   7   Entity ........................................................42
+   7.1   Entity Header Fields ........................................42
+   7.2   Entity Body .................................................43
+   7.2.1    Type .....................................................43
+   7.2.2    Entity Length ............................................43
+   8   Connections ...................................................44
+   8.1   Persistent Connections ......................................44
+   8.1.1    Purpose ..................................................44
+   8.1.2    Overall Operation ........................................45
+   8.1.3    Proxy Servers ............................................46
+   8.1.4    Practical Considerations .................................46
+   8.2   Message Transmission Requirements ...........................47
+   8.2.1    Persistent Connections and Flow Control ..................47
+   8.2.2    Monitoring Connections for Error Status Messages .........48
+   8.2.3    Use of the 100 (Continue) Status .........................48
+   8.2.4    Client Behavior if Server Prematurely Closes Connection ..50
+   9   Method Definitions ............................................51
+   9.1   Safe and Idempotent Methods .................................51
+   9.1.1    Safe Methods .............................................51
+   9.1.2    Idempotent Methods .......................................51
+   9.2   OPTIONS .....................................................52
+   9.3   GET .........................................................53
+   9.4   HEAD ........................................................54
+   9.5   POST ........................................................54
+   9.6   PUT .........................................................55
+   9.7   DELETE ......................................................56
+   9.8   TRACE .......................................................56
+   9.9   CONNECT .....................................................57
+   10   Status Code Definitions ......................................57
+   10.1  Informational 1xx ...........................................57
+   10.1.1   100 Continue .............................................58
+   10.1.2   101 Switching Protocols ..................................58
+   10.2  Successful 2xx ..............................................58
+   10.2.1   200 OK ...................................................58
+   10.2.2   201 Created ..............................................59
+   10.2.3   202 Accepted .............................................59
+   10.2.4   203 Non-Authoritative Information ........................59
+   10.2.5   204 No Content ...........................................60
+   10.2.6   205 Reset Content ........................................60
+   10.2.7   206 Partial Content ......................................60
+   10.3  Redirection 3xx .............................................61
+   10.3.1   300 Multiple Choices .....................................61
+   10.3.2   301 Moved Permanently ....................................62
+   10.3.3   302 Found ................................................62
+   10.3.4   303 See Other ............................................63
+   10.3.5   304 Not Modified .........................................63
+   10.3.6   305 Use Proxy ............................................64
+   10.3.7   306 (Unused) .............................................64
+   10.3.8   307 Temporary Redirect ...................................65
+   10.4  Client Error 4xx ............................................65
+   10.4.1    400 Bad Request .........................................65
+   10.4.2    401 Unauthorized ........................................66
+   10.4.3    402 Payment Required ....................................66
+   10.4.4    403 Forbidden ...........................................66
+   10.4.5    404 Not Found ...........................................66
+   10.4.6    405 Method Not Allowed ..................................66
+   10.4.7    406 Not Acceptable ......................................67
+   10.4.8    407 Proxy Authentication Required .......................67
+   10.4.9    408 Request Timeout .....................................67
+   10.4.10   409 Conflict ............................................67
+   10.4.11   410 Gone ................................................68
+   10.4.12   411 Length Required .....................................68
+   10.4.13   412 Precondition Failed .................................68
+   10.4.14   413 Request Entity Too Large ............................69
+   10.4.15   414 Request-URI Too Long ................................69
+   10.4.16   415 Unsupported Media Type ..............................69
+   10.4.17   416 Requested Range Not Satisfiable .....................69
+   10.4.18   417 Expectation Failed ..................................70
+   10.5  Server Error 5xx ............................................70
+   10.5.1   500 Internal Server Error ................................70
+   10.5.2   501 Not Implemented ......................................70
+   10.5.3   502 Bad Gateway ..........................................70
+   10.5.4   503 Service Unavailable ..................................70
+   10.5.5   504 Gateway Timeout ......................................71
+   10.5.6   505 HTTP Version Not Supported ...........................71
+   11   Access Authentication ........................................71
+   12   Content Negotiation ..........................................71
+   12.1  Server-driven Negotiation ...................................72
+   12.2  Agent-driven Negotiation ....................................73
+   12.3  Transparent Negotiation .....................................74
+   13   Caching in HTTP ..............................................74
+   13.1.1   Cache Correctness ........................................75
+   13.1.2   Warnings .................................................76
+   13.1.3   Cache-control Mechanisms .................................77
+   13.1.4   Explicit User Agent Warnings .............................78
+   13.1.5   Exceptions to the Rules and Warnings .....................78
+   13.1.6   Client-controlled Behavior ...............................79
+   13.2  Expiration Model ............................................79
+   13.2.1   Server-Specified Expiration ..............................79
+   13.2.2   Heuristic Expiration .....................................80
+   13.2.3   Age Calculations .........................................80
+   13.2.4   Expiration Calculations ..................................83
+   13.2.5   Disambiguating Expiration Values .........................84
+   13.2.6   Disambiguating Multiple Responses ........................84
+   13.3  Validation Model ............................................85
+   13.3.1   Last-Modified Dates ......................................86
+   13.3.2   Entity Tag Cache Validators ..............................86
+   13.3.3   Weak and Strong Validators ...............................86
+   13.3.4   Rules for When to Use Entity Tags and Last-Modified Dates.89
+   13.3.5   Non-validating Conditionals ..............................90
+   13.4  Response Cacheability .......................................91
+   13.5  Constructing Responses From Caches ..........................92
+   13.5.1   End-to-end and Hop-by-hop Headers ........................92
+   13.5.2   Non-modifiable Headers ...................................92
+   13.5.3   Combining Headers ........................................94
+   13.5.4   Combining Byte Ranges ....................................95
+   13.6  Caching Negotiated Responses ................................95
+   13.7  Shared and Non-Shared Caches ................................96
+   13.8  Errors or Incomplete Response Cache Behavior ................97
+   13.9  Side Effects of GET and HEAD ................................97
+   13.10   Invalidation After Updates or Deletions ...................97
+   13.11   Write-Through Mandatory ...................................98
+   13.12   Cache Replacement .........................................99
+   13.13   History Lists .............................................99
+   14   Header Field Definitions ....................................100
+   14.1  Accept .....................................................100
+   14.2  Accept-Charset .............................................102
+   14.3  Accept-Encoding ............................................102
+   14.4  Accept-Language ............................................104
+   14.5  Accept-Ranges ..............................................105
+   14.6  Age ........................................................106
+   14.7  Allow ......................................................106
+   14.8  Authorization ..............................................107
+   14.9  Cache-Control ..............................................108
+   14.9.1   What is Cacheable .......................................109
+   14.9.2   What May be Stored by Caches ............................110
+   14.9.3   Modifications of the Basic Expiration Mechanism .........111
+   14.9.4   Cache Revalidation and Reload Controls ..................113
+   14.9.5   No-Transform Directive ..................................115
+   14.9.6   Cache Control Extensions ................................116
+   14.10   Connection ...............................................117
+   14.11   Content-Encoding .........................................118
+   14.12   Content-Language .........................................118
+   14.13   Content-Length ...........................................119
+   14.14   Content-Location .........................................120
+   14.15   Content-MD5 ..............................................121
+   14.16   Content-Range ............................................122
+   14.17   Content-Type .............................................124
+   14.18   Date .....................................................124
+   14.18.1   Clockless Origin Server Operation ......................125
+   14.19   ETag .....................................................126
+   14.20   Expect ...................................................126
+   14.21   Expires ..................................................127
+   14.22   From .....................................................128
+   14.23   Host .....................................................128
+   14.24   If-Match .................................................129
+   14.25   If-Modified-Since ........................................130
+   14.26   If-None-Match ............................................132
+   14.27   If-Range .................................................133
+   14.28   If-Unmodified-Since ......................................134
+   14.29   Last-Modified ............................................134
+   14.30   Location .................................................135
+   14.31   Max-Forwards .............................................136
+   14.32   Pragma ...................................................136
+   14.33   Proxy-Authenticate .......................................137
+   14.34   Proxy-Authorization ......................................137
+   14.35   Range ....................................................138
+   14.35.1    Byte Ranges ...........................................138
+   14.35.2    Range Retrieval Requests ..............................139
+   14.36   Referer ..................................................140
+   14.37   Retry-After ..............................................141
+   14.38   Server ...................................................141
+   14.39   TE .......................................................142
+   14.40   Trailer ..................................................143
+   14.41  Transfer-Encoding..........................................143
+   14.42   Upgrade ..................................................144
+   14.43   User-Agent ...............................................145
+   14.44   Vary .....................................................145
+   14.45   Via ......................................................146
+   14.46   Warning ..................................................148
+   14.47   WWW-Authenticate .........................................150
+   15 Security Considerations .......................................150
+   15.1      Personal Information....................................151
+   15.1.1   Abuse of Server Log Information .........................151
+   15.1.2   Transfer of Sensitive Information .......................151
+   15.1.3   Encoding Sensitive Information in URI's .................152
+   15.1.4   Privacy Issues Connected to Accept Headers ..............152
+   15.2  Attacks Based On File and Path Names .......................153
+   15.3  DNS Spoofing ...............................................154
+   15.4  Location Headers and Spoofing ..............................154
+   15.5  Content-Disposition Issues .................................154
+   15.6  Authentication Credentials and Idle Clients ................155
+   15.7  Proxies and Caching ........................................155
+   15.7.1    Denial of Service Attacks on Proxies....................156
+   16   Acknowledgments .............................................156
+   17   References ..................................................158
+   18   Authors' Addresses ..........................................162
+   19   Appendices ..................................................164
+   19.1  Internet Media Type message/http and application/http ......164
+   19.2  Internet Media Type multipart/byteranges ...................165
+   19.3  Tolerant Applications ......................................166
+   19.4  Differences Between HTTP Entities and RFC 2045 Entities ....167
+   19.4.1   MIME-Version ............................................167
+   19.4.2   Conversion to Canonical Form ............................167
+   19.4.3   Conversion of Date Formats ..............................168
+   19.4.4   Introduction of Content-Encoding ........................168
+   19.4.5   No Content-Transfer-Encoding ............................168
+   19.4.6   Introduction of Transfer-Encoding .......................169
+   19.4.7   MHTML and Line Length Limitations .......................169
+   19.5  Additional Features ........................................169
+   19.5.1   Content-Disposition .....................................170
+   19.6  Compatibility with Previous Versions .......................170
+   19.6.1   Changes from HTTP/1.0 ...................................171
+   19.6.2   Compatibility with HTTP/1.0 Persistent Connections ......172
+   19.6.3   Changes from RFC 2068 ...................................172
+   20   Index .......................................................175
+   21   Full Copyright Statement ....................................176
 
 1 Introduction
 
@@ -300,7 +320,7 @@
    messages, containing metainformation about the data transferred and
    modifiers on the request/response semantics. However, HTTP/1.0 does
    not sufficiently take into consideration the effects of hierarchical
-   proxies, caching, the need for persistent connections, and virtual
+   proxies, caching, the need for persistent connections, or virtual
    hosts. In addition, the proliferation of incompletely-implemented
    applications calling themselves "HTTP/1.0" has necessitated a
    protocol version change in order for two communicating applications
@@ -312,13 +332,14 @@
 
    Practical information systems require more functionality than simple
    retrieval, including search, front-end update, and annotation. HTTP
-   allows an open-ended set of methods that indicate the purpose of a request.
+   allows an open-ended set of methods and headers that indicate the  purpose of a request [47].
It builds on the discipline of reference provided by the Uniform Resource Identifier (URI) [3]
-  [20]
, as a location (URL) [4] or name (URN) 
+ [20]
, for indicating the resource to which a method is to be applied. Messages are passed in a format similar to that used by Internet mail
+   [9]
as defined by the Multipurpose Internet Mail Extensions (MIME)
-  .
+   [7].

    HTTP is also used as a generic protocol for communication between
    user agents and proxies/gateways to other Internet systems, including
@@ -328,32 +349,17 @@
 
 1.2 Requirements
 
-   This specification uses the same words as RFC 1123 [8] for defining
-   the significance of each particular requirement. These words are:
-
-   MUST
-      This word or the adjective "required" means that the item is an
-      absolute requirement of the specification.
-
-   SHOULD
-      This word or the adjective "recommended" means that there may
-      exist valid reasons in particular circumstances to ignore this
-      item, but the full implications should be understood and the case
-      carefully weighed before choosing a different course.
-
-   MAY
-      This word or the adjective "optional" means that this item is
-      truly optional. One vendor may choose to include the item because
-      a particular marketplace requires it or because it enhances the
-      product, for example; another vendor may omit the same item.
+   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
+   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
+   document are to be interpreted as described in RFC 2119 [34].
 
    An implementation is not compliant if it fails to satisfy one or more
-   of the MUST
+   of the MUST or REQUIRED level
requirements for the protocols it implements. An implementation that satisfies all the MUST
-   and all the SHOULD
+   or REQUIRED level and all the SHOULD level
requirements for its protocols is said to be "unconditionally compliant"; one that satisfies all the MUST
-   requirements but not all the SHOULD
+   level requirements but not all the SHOULD level
requirements for its protocols is said to be "conditionally compliant."
 
 1.3 Terminology
 
@@ -378,7 +384,7 @@
    resource
       A network data object or service that can be identified by a URI,
       as defined in section 3.2. Resources may be available in multiple
representations (e.g. multiple languages, data formats, size,
+      and
       resolutions) or vary in other ways.
 
    entity
@@ -401,7 +407,7 @@
    variant
       A resource may have one, or more than one, representation(s)
       associated with it at any given instant. Each of these
-      representations is termed a `variant.' Use of the term `variant'
+      representations is termed a `varriant'.  Use of the term `variant'
;;Each of these representations is termed a `variant'. Use of the term `variant' [INS[RFC Errata by RFC Editor]]
       does not necessarily imply that the resource is subject to content
       negotiation.
 
@@ -419,7 +425,7 @@
       be capable of being both a client and a server; our use of these
       terms refers only to the role being performed by the program for a
       particular connection, rather than to the program's capabilities
in general. Likewise, any server may act as an origin server,
       proxy, gateway, or tunnel, switching behavior based on the nature
       of each request.
 
@@ -430,8 +436,17 @@
       An intermediary program which acts as both a server and a client
       for the purpose of making requests on behalf of other clients.
       Requests are serviced internally or by passing them on, with
-      possible translation, to other servers. A proxy must implement
+      possible translation, to other servers. A proxy MUST implement
both the client and server requirements of this specification.
+      A "transparent proxy" is a proxy that does not modify the request or
+      response beyond what is required for proxy authentication and
+      identification. A "non-transparent proxy" is a proxy that modifies
+      the request or response in order to provide some added service to
+      the user agent, such as group annotation services, media type
+      transformation, protocol reduction, or anonymity filtering. Except
+      where either transparent or non-transparent behavior is explicitly
+      stated, the HTTP proxy requirements apply to both types of
+      proxies.
 
    gateway
       A server which acts as an intermediary for some other server.
@@ -449,16 +464,16 @@
    cache
       A program's local store of response messages and the subsystem
       that controls its message storage, retrieval, and deletion. A
-      cache stores cachable responses in order to reduce the response
+      cache stores cacheable responses in order to reduce the response
       time and network bandwidth consumption on future, equivalent
       requests. Any client or server may include a cache, though a cache
       cannot be used by a server that is acting as a tunnel.
 
-   cachable
+   cacheable
-      A response is cachable if a cache is allowed to store a copy of
+      A response is cacheable if a cache is allowed to store a copy of
       the response message for use in answering subsequent requests. The
-      rules for determining the cachability of HTTP responses are
+      rules for determining the cacheability of HTTP responses are
-      defined in section 13. Even if a resource is cachable, there may
+      defined in section 13. Even if a resource is cacheable, there may
       be additional constraints on whether a cache can use the cached
       copy for a particular request.
 
@@ -505,6 +520,15 @@
       that is used to find out whether a cache entry is an equivalent
       copy of an entity.
 
+   upstream/downstream
+      Upstream and downstream describe the flow of a message: all
+      messages flow from upstream to downstream.
+
+   inbound/outbound
+      Inbound and outbound refer to the request and response paths for
+      messages: "inbound" means "traveling toward the origin server",
+      and "outbound" means "traveling toward the user agent"
+
 1.4 Overall Operation
 
    The HTTP protocol is a request/response protocol. A client sends a
@@ -522,9 +546,9 @@
    simplest case, this may be accomplished via a single connection (v)
    between the user agent (UA) and the origin server (O).
 
   request chain ------------------------>
UA -------------------v------------------- O
   <----------------------- response chain
 
    A more complicated situation occurs when one or more intermediaries
    are present in the request/response chain. There are three common
@@ -540,19 +564,20 @@
    firewall) even when the intermediary cannot understand the contents
    of the messages.
 
   request chain -------------------------------------->
UA -----v----- A -----v----- B -----v----- C -----v----- O
   <------------------------------------- response chain
 
    The figure above shows three intermediaries (A, B, and C) between the
    user agent and origin server. A request or response message that
    travels the whole chain will pass through four separate connections.
    This distinction is important because some HTTP communication options
    may apply only to the connection with the nearest, non-tunnel
    neighbor, only to the end-points of the chain, or to all connections
along the chain. Although the diagram is linear, each participant may
be engaged in multiple, simultaneous communications. For example, B
may be receiving requests from many clients other than A, and/or
    forwarding requests to servers other than C, at the same time that it
    is handling A's request.
 
@@ -564,18 +589,18 @@
    cached copy of an earlier response from O (via C) for a request which
    has not been cached by UA or A.
 
   request chain ---------->
UA -----v----- A -----v----- B - - - - - - C - - - - - - O
   <--------- response chain
 
-   Not all responses are usefully cachable, and some requests may
+   Not all responses are usefully cacheable, and some requests may
    contain modifiers which place special requirements on cache behavior.
-   HTTP requirements for cache behavior and cachable responses are
+   HTTP requirements for cache behavior and cacheable responses are
    defined in section 13.
 
    In fact, there are a wide variety of architectures and configurations
    of caches and proxies currently being experimented with or deployed
-   across the World Wide Web; these systems include national hierarchies
+   across the World Wide Web. These systems include national hierarchies
    of proxy caches to save transoceanic bandwidth, systems that
    broadcast or multicast cache entries, organizations that distribute
    subsets of cached data via CD-ROM, and so on. HTTP systems are used
@@ -588,9 +613,9 @@
    failure.
 
    HTTP communication usually takes place over TCP/IP connections. The
-   default port is TCP 80, but other ports can be used.
+   default port is TCP 80 [19], but other ports can be used.
This does not preclude HTTP from being implemented on top of any other protocol
on the Internet, or on other networks. HTTP only presumes a reliable
    transport; any protocol that provides such guarantees can be used;
    the mapping of the HTTP/1.1 request and response structures onto the
    transport data units of the protocol in question is outside the scope
@@ -607,80 +632,84 @@
 
    All of the mechanisms specified in this document are described in
    both prose and an augmented Backus-Naur Form (BNF) similar to that
-   used by RFC 822 [9]. Implementers will need to be familiar with the
+   used by RFC 822 [9]. Implementors will need to be familiar with the
    notation in order to understand this specification. The augmented BNF
    includes the following constructs:

name = definition
The name of a rule is simply the name itself (without any enclosing
"<" and ">") and is separated from its definition by the equal "=" character.
-     Whitespace
+     White space
is only significant in that  indentation of continuation lines is used to indicate a rule
definition that spans more than one line. Certain basic rules are
in uppercase, such as SP, LWS, HT, CRLF, DIGIT, ALPHA, etc. Angle
brackets are used within definitions whenever their presence will facilitate
discerning the use of rule names.

"literal"
Quotation marks surround literal text. Unless stated otherwise, the text is case-insensitive.

rule1 | rule2
Elements separated by a bar ("|") are alternatives, e.g., "yes | no" will accept yes or no.

(rule1 rule2)
Elements enclosed in parentheses are treated as a single element.
Thus, "(elem (foo | bar) elem)" allows the token sequences "elem foo elem" and "elem bar elem".

*rule
The character "*" preceding an element indicates repetition. The
full form is "<n>*<m>element" indicating at least <n> and at most
<m> occurrences of element. Default values are 0 and infinity so
that "*(element)" allows any number, including zero; "1*element"
requires at least one; and "1*2element" allows one or two.

[rule]
Square brackets enclose optional elements; "[foo bar]" is
equivalent to "*1(foo bar)".

N rule
Specific repetition: "<n>(element)" is equivalent to
"<n>*<n>(element)"; that is, exactly <n> occurrences of (element).
Thus 2DIGIT is a 2-digit number, and 3ALPHA is a string of three
alphabetic characters.

#rule
A construct "#" is defined, similar to "*", for defining lists of
elements. The full form is "<n>#<m>element " indicating at least
<n> and at most <m> elements, each separated by one or more commas
-     (",") and optional linear whitespace (LWS). This makes the usual
+      (",") and OPTIONAL linear white space (LWS). This makes the usual
-     form of lists very easy; a rule such as "( *LWS element *( *LWS ","
+      form of lists very easy; a rule such as
-     *LWS element )) " can be shown as "1#element".
+         ( *LWS element *( *LWS "," *LWS element ))
+      can be shown as
+         1#element
Wherever this construct is used, null elements are allowed, but do not
contribute to the count of elements present. That is, "(element), , (element) " is permitted,
but counts as only two elements. Therefore, where
at least one element is required, at least one non-null element
-     must be present.
+      MUST be present.
Default values are 0 and infinity so that "#element" allows any number, including zero;
"1#element" requires at least one; and "1#2element" allows one or two.

; comment
A semi-colon, set off some distance to the right of rule text,
starts a comment that continues to the end of line. This is a
simple way of including useful notes in parallel with the specifications.

implied *LWS
The grammar described by this specification is word-based. Except
-     where noted otherwise, linear whitespace (LWS) can be included
+      where noted otherwise, linear white space (LWS) can be included
between any two adjacent words (token or quoted-string), and
-     between adjacent tokens and delimiters (tspecials),
+      between adjacent words and separators,
without changing the interpretation of a field. At least one delimiter
-     (tspecials) must exist between any two tokens,
+      (LWS and/or separators) MUST exist between any two tokens (for the definition of "token" below),
since they would otherwise be interpreted as a single token.
 
 2.2 Basic Rules
 
@@ -688,58 +717,63 @@
    describe basic parsing constructs. The US-ASCII coded character set
    is defined by ANSI X3.4-1986 [21].

OCTET          = <any 8-bit sequence of data>
CHAR           = <any US-ASCII character (octets 0 - 127)>
UPALPHA        = <any US-ASCII uppercase letter "A".."Z">
LOALPHA        = <any US-ASCII lowercase letter "a".."z">
ALPHA          = UPALPHA | LOALPHA
DIGIT          = <any US-ASCII digit "0".."9">
CTL            = <any US-ASCII control character (octets 0 - 31) and DEL (127)>
CR             = <US-ASCII CR, carriage return (13)>
LF             = <US-ASCII LF, linefeed (10)>
SP             = <US-ASCII SP, space (32)>
HT             = <US-ASCII HT, horizontal-tab (9)>
<">            = <US-ASCII double-quote mark (34)>
 
    HTTP/1.1 defines the sequence CR LF as the end-of-line marker for all
    protocol elements except the entity-body (see appendix 19.3 for
    tolerant applications). The end-of-line marker within an entity-body
    is defined by its associated media type, as described in section 3.7.

CRLF           = CR LF
 
-   HTTP/1.1 headers can be folded onto multiple lines if the
+   HTTP/1.1 header field values can be folded onto multiple lines if the
    continuation line begins with a space or horizontal tab. All linear
white space, including folding, has the same semantics as SP.
+   A recipient MAY replace any linear white space with a single SP before
+   interpreting the field value or forwarding the message downstream.

LWS            = [CRLF] 1*( SP | HT )
 
    The TEXT rule is only used for descriptive field contents and values
    that are not intended to be interpreted by the message parser. Words
-   of *TEXT may contain characters from character sets other than
+   of *TEXT MAY contain characters from character sets other than 
-   ISO 8859-1 [22] only when encoded according to the rules of RFC 1522
+   ISO-8859-1 [22] only when encoded according to the rules of RFC 2047
    [14].
 
TEXT           = <any OCTET except CTLs, but including LWS>

+   A CRLF is allowed in the definition of TEXT only as part of a header
+   field continuation. It is expected that the folding LWS will be
+   replaced with a single SP before interpretation of the TEXT value.
 
    Hexadecimal numeric characters are used in several protocol elements.

HEX            = "A" | "B" | "C" | "D" | "E" | "F" | "a" | "b" | "c" | "d" | "e" | "f" | DIGIT

    Many HTTP/1.1 header field values consist of words separated by LWS
    or special characters. These special characters MUST be in a quoted
-   string to be used within a parameter value.
+   string to be used within a parameter value
+  (as defined in section  3.6).
 
-          token          = 1*<any CHAR except CTLs or tspecials>
+       token          = 1*<any CHAR except CTLs or separators>
-
-          tspecials      = "(" | ")" | "<" | ">" | "@"
-                         | "," | ";" | ":" | "\" | <">
-                         | "/" | "[" | "]" | "?" | "="
-                         | "{" | "}" | SP | HT
+       separators     = "(" | ")" | "<" | ">" | "@"
+                      | "," | ";" | ":" | "\" | <">
+                      | "/" | "[" | "]" | "?" | "="
+                      | "{" | "}" | SP | HT
 
    Comments can be included in some HTTP header fields by surrounding
    the comment text with parentheses. Comments are only allowed in
@@ -747,20 +781,19 @@
    In all other fields, parentheses are considered part of the field
    value.
 
-          comment        = "(" *( ctext | comment ) ")"
+       comment        = "(" *( ctext | quoted-pair | comment ) ")"
ctext          = <any TEXT excluding "(" and ")">
 
    A string of text is parsed as a single word if it is quoted using
    double-quote marks.
 
-          quoted-string  = ( <"> *(qdtext) <"> )
+       quoted-string  = ( <"> *(qdtext | quoted-pair ) <"> )
qdtext         = <any TEXT except <">>
 
-   The backslash character ("\") may
+   The backslash character ("\") MAY
be used as a single-character quoting mechanism only within quoted-string and comment constructs.

quoted-pair    = "\" CHAR
 
 3 Protocol Parameters
 
@@ -778,99 +811,69 @@
    algorithm, but which may add to the message semantics and imply
    additional capabilities of the sender. The <major> number is
    incremented when the format of a message within the protocol is changed.
+   See RFC 2145 [36] for a fuller explanation.
 
    The version of an HTTP message is indicated by an HTTP-Version field
    in the first line of the message. [INS[[INS[{errata}]] HTTP-Version is case-sensitive.]]

HTTP-Version   = "HTTP" "/" 1*DIGIT "." 1*DIGIT
 
    Note that the major and minor numbers MUST be treated as separate
-   integers and that each may be incremented higher than a single digit.
+   integers and that each MAY be incremented higher than a single digit.
    Thus, HTTP/2.4 is a lower version than HTTP/2.13, which in turn is
    lower than HTTP/12.3. Leading zeros MUST be ignored by recipients and
    MUST NOT be sent.
 
-   Applications sending Request or Response messages, as defined by this
-   specification, MUST include an HTTP-Version of "HTTP/1.1". Use of
-   this version number indicates that the sending application is at
-   least conditionally compliant with this specification.
+   An application that sends a request or response message that includes
+   HTTP-Version of "HTTP/1.1" MUST be at least conditionally compliant
+   with this specification. Applications that are at least conditionally
+   compliant with this specification SHOULD use an HTTP-Version of
+   "HTTP/1.1" in their messages, and MUST do so for any message that is
+   not compatible with HTTP/1.0. For more details on when to send
+   specific HTTP-Version values, see RFC 2145 [36].
 
    The HTTP version of an application is the highest HTTP version for
    which the application is at least conditionally compliant.
 
-   Proxy and gateway applications must be careful when forwarding
+   Proxy and gateway applications need to be careful when forwarding
    messages in protocol versions different from that of the application.
    Since the protocol version indicates the protocol capability of the
-   sender, a proxy/gateway MUST never send a message with a version
+   sender, a proxy/gateway MUST NOT send a message with a version
-   indicator which is greater than its actual version; if a higher
+   indicator which is greater than its actual version. If a higher
    version request is received, the proxy/gateway MUST either downgrade
-   the request version,
+   the request version, or
respond with an error, or switch to tunnel behavior.
-   Requests with a version lower than that of the proxy/gateway's version MAY be upgraded before being forwarded; the
-   proxy/gateway's response to that request MUST be in the same major
-   version as the request.
 
+   Due to interoperability problems with HTTP/1.0 proxies discovered
+   since the publication of RFC 2068[33], caching proxies MUST, gateways
+   MAY, and tunnels MUST NOT upgrade the request to the highest version
+   they support. The proxy/gateway's response to that request MUST be in
+   the same major version as the request.

Note: Converting between versions of HTTP may involve modification
of header fields required or forbidden by the versions involved.
 
 3.2 Uniform Resource Identifiers
 
    URIs have been known by many names: WWW addresses, Universal Document
-   Identifiers, Universal Resource Identifiers , and finally the
+   Identifiers, Universal Resource Identifiers [3], and finally the
-   combination of Uniform Resource Locators (URL)  and Names (URN).
+   combination of Uniform Resource Locators (URL) [4] and Names (URN)  [20].
As far as HTTP is concerned, Uniform Resource Identifiers are simply
formatted strings which identify--via name, location, or any
other characteristic--a resource.
 
 3.2.1 General Syntax
 
    URIs in HTTP can be represented in absolute form or relative to some
-   known base URI, depending upon the context of their use. The two
+   known base URI [11], depending upon the context of their use. The two
    forms are differentiated by the fact that absolute URIs always begin
with a scheme name followed by a colon.
+   For definitive information on
+   URL syntax and semantics, see "Uniform Resource Identifiers (URI):
+   Generic Syntax and Semantics," RFC 2396 [42] (which replaces RFCs
+   1738 [4] and RFC 1808 [11]). This specification adopts the
+   definitions of "URI-reference", "absoluteURI", "relativeURI", "port",
+   "host","abs_path", "rel_path", and "authority" from that
+   specification.
-
-          URI            = ( absoluteURI | relativeURI ) [ "#" fragment ]
-
-          absoluteURI    = scheme ":" *( uchar | reserved )
-
-          relativeURI    = net_path | abs_path | rel_path
-
-          net_path       = "//" net_loc [ abs_path ]
-          abs_path       = "/" rel_path
-          rel_path       = [ path ] [ ";" params ] [ "?" query ]
-
-          path           = fsegment *( "/" segment )
-          fsegment       = 1*pchar
-          segment        = *pchar
-
-          params         = param *( ";" param )
-          param          = *( pchar | "/" )
-
-          scheme         = 1*( ALPHA | DIGIT | "+" | "-" | "." )
-          net_loc        = *( pchar | ";" | "?" )
-
-          query          = *( uchar | reserved )
-          fragment       = *( uchar | reserved )
-
-          pchar          = uchar | ":" | "@" | "&" | "=" | "+"
-          uchar          = unreserved | escape
-          unreserved     = ALPHA | DIGIT | safe | extra | national
-
-          escape         = "%" HEX HEX
-          reserved       = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+"
-          extra          = "!" | "*" | "'" | "(" | ")" | ","
-          safe           = "$" | "-" | "_" | "."
-          unsafe         = CTL | SP | <"> | "#" | "%" | "<" | ">"
-          national       = <any OCTET excluding ALPHA, DIGIT,
-                           reserved, extra, safe, and unsafe>
-
-   For definitive information on URL syntax and semantics, see RFC 1738
-   [4] and RFC 1808 [11]. The BNF above includes national characters not
-   allowed in valid URLs as specified by RFC 1738, since HTTP servers
-   are not restricted in the set of unreserved characters allowed to
-   represent the rel_path part of addresses, and HTTP proxies may
-   receive requests for URIs not defined by RFC 1738.
 
    The HTTP protocol does not place any a priori limit on the length of
    a URI. Servers MUST be able to handle the URI of any resource they
@@ -879,9 +882,9 @@
    SHOULD return 414 (Request-URI Too Long) status if a URI is longer
    than the server can handle (see section 10.4.15).
 
-     Note: Servers should be cautious about depending on URI lengths
+   Note: Servers ought to be cautious about depending on URI lengths
above 255 bytes, because some older client or proxy
implementations might not properly support these lengths.
 
 3.2.2 http URL
 
@@ -889,22 +892,19 @@
    protocol. This section defines the scheme-specific syntax and
    semantics for http URLs.
 
-
-          http_URL       = "http:" "//" host [ ":" port ] [ abs_path ]
+   http_URL = "http:" "//" host [ ":" port ] [ abs_path [ "?" query ]]
-
-          host           = <A legal Internet host domain name
-                            or IP address (in dotted-decimal form),
-                            as defined by Section 2.1 of RFC 1123>
-
-          port           = *DIGIT
 
    If the port is empty or not given, port 80 is assumed. The semantics
    are that the identified resource is located at the server listening
    for TCP connections on that port of that host, and the Request-URI
-   for the resource is abs_path.
+   for the resource is abs_path (section 5.1.2).
-   The use of IP addresses in URL's SHOULD be avoided whenever possible (see RFC 1900 [24]).
+   The use of IP addresses in URLs SHOULD be avoided whenever possible (see RFC 1900 [24]).
If the abs_path is not present in the URL, it MUST be given as "/" when used as a
Request-URI for a resource (section 5.1.2).
+   If a proxy receives a host name which is not a fully qualified domain name, it
+   MAY add its domain to the host name it received. If a proxy receives
+   a fully qualified domain name, the proxy MUST NOT change the host
+   name.
 
 3.2.3 URI Comparison
 
@@ -912,25 +912,23 @@
    SHOULD use a case-sensitive octet-by-octet comparison of the entire
    URIs, with these exceptions:
 
-     o  A port that is empty or not given is equivalent to the default
+      - A port that is empty or not given is equivalent to the default
-        port for that URI;
+        port for that URI-reference;
 
-     o  Comparisons of host names MUST be case-insensitive;
+      - Comparisons of host names MUST be case-insensitive;
 
-     o  Comparisons of scheme names MUST be case-insensitive;
+      - Comparisons of scheme names MUST be case-insensitive;
 
-     o  An empty abs_path is equivalent to an abs_path of "/".
+      - An empty abs_path is equivalent to an abs_path of "/".
 
    Characters other than those in the "reserved" [DEL[and "unsafe"]] set[DEL[s]] [INS[(removed by errata)]] (see
- section 3.2)
+   RFC 2396 [42])
are equivalent to their ""%" HEX HEX" encoding.
 
    For example, the following three URIs are equivalent:
 
http://abc.com:80/~smith/home.html
http://ABC.com/%7Esmith/home.html
http://ABC.com:/%7esmith/home.html
 
 3.3 Date/Time Formats
 
@@ -939,59 +937,57 @@
    HTTP applications have historically allowed three different formats
    for the representation of date/time stamps:
 
Sun, 06 Nov 1994 08:49:37 GMT  ; RFC 822, updated by RFC 1123
Sunday, 06-Nov-94 08:49:37 GMT ; RFC 850, obsoleted by RFC 1036
Sun Nov  6 08:49:37 1994       ; ANSI C's asctime() format
 
    The first format is preferred as an Internet standard and represents
-   a fixed-length subset of that defined by RFC 1123  (an update to RFC 822). 
+   a fixed-length subset of that defined by RFC 1123 [8] (an update to RFC 822 [9]).
The second format is in common use, but is based on the
    obsolete RFC 850 [12] date format and lacks a four-digit year.
    HTTP/1.1 clients and servers that parse the date value MUST accept
    all three formats (for compatibility with HTTP/1.0), though they MUST
    only generate the RFC 1123 format for representing HTTP-date values in header fields.
+   See section 19.3 for further information.
 
Note: Recipients of date values are encouraged to be robust in
accepting date values that may have been sent by non-HTTP
applications, as is sometimes the case when retrieving or posting
messages via proxies/gateways to SMTP or NNTP.
 
    All HTTP date/time stamps MUST be represented in Greenwich Mean Time
(GMT), without exception.
+   For the purposes of HTTP, GMT is exactly equal to UTC (Coordinated Universal Time).
This is indicated in the first two formats by the inclusion of "GMT" as the three-letter abbreviation for time
zone, and MUST be assumed when reading the asctime format.
+   HTTP-date is case sensitive and MUST NOT include
+   additional LWS beyond that specifically included as SP in the
+   grammar.
-
HTTP-date    = rfc1123-date | rfc850-date | asctime-date
rfc1123-date = wkday "," SP date1 SP time SP "GMT"
rfc850-date  = weekday "," SP date2 SP time SP "GMT"
asctime-date = wkday SP date3 SP time SP 4DIGIT
date1        = 2DIGIT SP month SP 4DIGIT
; day month year (e.g., 02 Jun 1982)
date2        = 2DIGIT "-" month "-" 2DIGIT
; day-month-year (e.g., 02-Jun-82)
date3        = month SP ( 2DIGIT | ( SP 1DIGIT ))
; month day (e.g., Jun  2)
time         = 2DIGIT ":" 2DIGIT ":" 2DIGIT
; 00:00:00 - 23:59:59
wkday        = "Mon" | "Tue" | "Wed" | "Thu" | "Fri" | "Sat" | "Sun"
weekday      = "Monday" | "Tuesday" | "Wednesday" | "Thursday" | "Friday" | "Saturday" | "Sunday"
month        = "Jan" | "Feb" | "Mar" | "Apr" | "May" | "Jun" | "Jul" | "Aug" | "Sep" | "Oct" | "Nov" | "Dec"

Note: HTTP requirements for the date/time stamp format apply only
to their usage within the protocol stream. Clients and servers are
not required to use these formats for user presentation, request
logging, etc.
 
 3.3.2 Delta Seconds
 
@@ -999,44 +995,63 @@
    integer number of seconds, represented in decimal, after the time
    that the message was received.
 
delta-seconds  = 1*DIGIT
 
 3.4 Character Sets
 
    HTTP uses the same definition of the term "character set" as that
    described for MIME:
 
The term "character set" is used in this document to refer to a
method used with one or more tables to convert a sequence of octets
into a sequence of characters. Note that unconditional conversion in
the other direction is not required, in that not all characters may
be available in a given character set and a character set may provide
more than one sequence of octets to represent a particular character.
This definition is intended to allow various kinds of character
encoding, from simple single-table mappings such as US-ASCII to
-      complex table switching methods such as those that use ISO2022's
+      complex table switching methods such as those that use ISO-2022's
techniques. However, the definition associated with a MIME character
set name MUST fully specify the mapping to be performed from octets
to characters. In particular, use of external profiling information
to determine the exact mapping is not permitted.

Note: This use of the term "character set" is more commonly
referred to as a "character encoding." However, since HTTP and MIME
share the same registry, it is important that the terminology
also be shared.
 
    HTTP character sets are identified by case-insensitive tokens. The
    complete set of tokens is defined by the IANA Character Set registry
    [19].
 
charset = token
 
    Although HTTP allows an arbitrary token to be used as a charset
    value, any token that has a predefined value within the IANA Character Set registry
+   [19]
MUST represent the character set defined by that registry. Applications SHOULD limit their use of character sets
to those defined by the IANA registry.

+   Implementors should be aware of IETF character set requirements [38] [41].

[INS[{errata}
HTTP uses charset in two contexts: within an Accept-Charset request header (in which the charset value is an unquoted token) and as the value of a parameter in a Content-type header (within a request or response), in which case the parameter value of the charset parameter may be quoted.
]INS]
+
+3.4.1 Missing Charset
+
+   Some HTTP/1.0 software has interpreted a Content-Type header without
+   charset parameter incorrectly to mean "recipient should guess."
+   Senders wishing to defeat this behavior MAY include a charset
+   parameter even when the charset is ISO-8859-1 and SHOULD do so when
+   it is known that it will not confuse the recipient.
+
+   Unfortunately, some older HTTP/1.0 clients did not deal properly with
+   an explicit charset parameter. HTTP/1.1 recipients MUST respect the
+   charset label provided by the sender; and those user agents that have
+   a provision to "guess" a charset MUST use the charset from the
+   content-type field if they support that charset, rather than the
+   recipient's preference, when initially displaying a document. See
+   section 3.7.1.
 
 3.5 Content Codings
 
@@ -1047,11 +1062,11 @@
    and without loss of information. Frequently, the entity is stored in
    coded form, transmitted directly, and only decoded by the recipient.
 
content-coding   = token
 
    All content-coding values are case-insensitive. HTTP/1.1 uses
    content-coding values in the Accept-Encoding (section 14.3) and
-   Content-Encoding (section 14.12) header fields. Although the value
+   Content-Encoding (section 14.11) header fields. Although the value
    describes the content-coding, what is more important is that it
    indicates what decoding mechanism will be required to remove the
    encoding.
@@ -1060,142 +1075,188 @@
    content-coding value tokens. Initially, the registry contains the
    following tokens:
 
gzip An encoding format produced by the file compression program "gzip"
(GNU zip) as described in RFC 1952 [25]. This format is a
Lempel-Ziv coding (LZ77) with a 32 bit CRC.
 
    compress
         The encoding format produced by the common UNIX file compression
         program "compress". This format is an adaptive Lempel-Ziv-Welch
         coding (LZW).
 
-     Note: 
Use of program names for the identification of encoding formats
-     is not desirable and should be discouraged for future
+     is not desirable and        is discouraged for future
encodings. Their use here is representative of historical practice,
not good design. For compatibility with previous implementations of HTTP, applications
-     should
+     SHOULD
consider "x-gzip" and "x-compress" to be equivalent to "gzip" and "compress" respectively.

deflate
The "zlib" format defined in RFC 1950 [31] in combination with
the "deflate" compression mechanism described in RFC 1951 [29].

+   identity
+        The default (identity) encoding; the use of no transformation
+        whatsoever. This content-coding is used only in the Accept-Encoding
+         header, and SHOULD NOT be used in the Content-Encoding
+        header.
 
-
-   New content-coding value tokens should be registered; to allow
+   New content-coding value tokens SHOULD be registered; to allow
    interoperability between clients and servers, specifications of the
-   content coding algorithms needed to implement a new value should be
+   content coding algorithms needed to implement a new value SHOULD be
    publicly available and adequate for independent implementation, and
    conform to the purpose of content coding defined in this section.
 
 3.6 Transfer Codings
 
-   Transfer coding values are used to indicate an encoding
+   Transfer-coding values are used to indicate an encoding
    transformation that has been, can be, or may need to be applied to an
    entity-body in order to ensure "safe transport" through the network.
-   This differs from a content coding in that the transfer coding is a
+   This differs from a content coding in that the transfer-coding is a
    property of the message, not of the original entity.
 
transfer-coding         = "chunked" | transfer-extension
-          transfer-extension      = token
+       transfer-extension      = token *( ";" parameter )
 
+   Parameters are in  the form of attribute/value pairs.
+
+       parameter               = attribute "=" value
+       attribute               = token
+       value                   = token | quoted-string
 
    All transfer-coding values are case-insensitive. HTTP/1.1 uses
-   transfer coding values
+   transfer-coding values in the TE header field (section 14.39) and
-   in the Transfer-Encoding header field (section 14.40).
+   in the Transfer-Encoding header field (section 14.41).
+
+   Whenever a transfer-coding is applied to a message-body, the set of
+   transfer-codings MUST include "chunked", unless the message is
+   terminated by closing the connection. When the "chunked" transfer-
+   coding is used, it MUST be the last transfer-coding applied to the
+   message-body. The "chunked" transfer-coding MUST NOT be applied more
+   than once to a message-body. These rules allow the recipient to
+   determine the transfer-length of the message (section 4.4).
 
-   Transfer codings are analogous to the Content-Transfer-Encoding
+   Transfer-codings are analogous to the Content-Transfer-Encoding
-   values of MIME , which were designed to enable safe transport of
+   values of MIME [7], which were designed to enable safe transport of
    binary data over a 7-bit transport service. However, safe transport
    has a different focus for an 8bit-clean transfer protocol. In HTTP,
    the only unsafe characteristic of message-bodies is the difficulty in
    determining the exact body length (section 7.2.2), or the desire to
    encrypt data over a shared transport.
 
+   The Internet Assigned Numbers Authority (IANA) acts as a registry for
+   transfer-coding value tokens. Initially, the registry contains the
+   following tokens: "chunked" (section 3.6.1), [DEL[[INS[{removed by errata}]] "identity" (section
+   3.6.2),]] "gzip" (section 3.5), "compress" (section 3.5), and "deflate"
+   (section 3.5).
+
+   New transfer-coding value tokens SHOULD be registered in the same way
+   as new content-coding value tokens (section 3.5).
+
+   A server which receives an entity-body with a transfer-coding it does
+   not understand SHOULD return 501 (Unimplemented), and close the
+   connection. A server MUST NOT send transfer-codings to an HTTP/1.0
+   client.
+
+3.6.1 Chunked Transfer Coding
+
    The chunked encoding modifies the body of a message in order to
    transfer it as a series of chunks, each with its own size indicator,
-   followed by an optional footer containing entity-header fields. This
+   followed by an OPTIONAL trailer containing entity-header fields. This
-   allows dynamically-produced content to be transferred along with the
+   allows dynamically produced content to be transferred along with the
    information necessary for the recipient to verify that it has
    received the full message.
 
        Chunked-Body   = *chunk
-                        "0" CRLF
-                        footer
+                        last-chunk
+                        trailer
                         CRLF
 
-       chunk          = chunk-size [ chunk-ext ] CRLF
+       chunk          = chunk-size [ chunk-extension ] CRLF
                         chunk-data CRLF
 
-       hex-no-zero    = <HEX excluding "0">
-
-       chunk-size     = hex-no-zero *HEX
+       chunk-size     = 1*HEX
+       last-chunk     = 1*("0") [ chunk-extension ] CRLF
-       chunk-ext      = *( ";" chunk-ext-name [ "=" chunk-ext-value ] )
+       chunk-extension= *( ";" chunk-ext-name [ "=" chunk-ext-val ] )
        chunk-ext-name = token
        chunk-ext-val  = token | quoted-string
        chunk-data     = chunk-size(OCTET)
 
-       footer         = *entity-header
+       trailer        = *(entity-header CRLF)
-
-   The chunked encoding is ended by a zero-sized chunk followed by the
-   footer, which is terminated by an empty line. The purpose of the
-   footer is to provide an efficient way to supply information about an
-   entity that is generated dynamically; applications MUST NOT send
-   header fields in the footer which are not explicitly defined as being
-   appropriate for the footer, such as Content-MD5 or future extensions
-   to HTTP for digital signatures or other facilities.
+   The chunk-size field is a string of hex digits indicating the size of
+   the chunk[INS[-data in octets [INS[{errata}]]]]. The chunked encoding is ended by any chunk whose size is
+   zero, followed by the trailer, which is terminated by an empty line.
+
+   The trailer allows the sender to include additional HTTP header
+   fields at the end of the message. The Trailer header field can be
+   used to indicate which header fields are included in a trailer (see
+   section 14.40).
+
+   A server using chunked transfer-coding in a response MUST NOT use the
+   trailer for any header fields unless at least one of the following is
+   true:
+
+   a)the request included a TE header field that indicates "trailers" is
+     acceptable in the transfer-coding of the  response, as described in
+     section 14.39; or,
+
+   b)the server is the origin server for the response, the trailer
+     fields consist entirely of optional metadata, and the recipient
+     could use the message (in a manner acceptable to the origin server)
+     without receiving this metadata.  In other words, the origin server
+     is willing to accept the possibility that the trailer fields might
+     be silently discarded along the path to the client.
+
+   This requirement prevents an interoperability failure when the
+   message is being received by an HTTP/1.1 (or later) proxy and
+   forwarded to an HTTP/1.0 recipient. It avoids a situation where
+   compliance with the protocol would have necessitated a possibly
+   infinite buffer on the proxy.
 
    An example process for decoding a Chunked-Body is presented in
    appendix 19.4.6.
 
    All HTTP/1.1 applications MUST be able to receive and decode the
-   "chunked" transfer coding, and MUST ignore transfer coding extensions
+   "chunked" transfer-coding, and MUST ignore chunk-extension extensions
they do not understand.
-   A server which receives an entity-body with a transfer-coding it does not understand SHOULD return 501
-   (Unimplemented), and close the connection. A server MUST NOT send
-   transfer-codings to an HTTP/1.0 client.
 
 3.7 Media Types
 
-   HTTP uses Internet Media Types  in the Content-Type (section 14.18)
+   HTTP uses Internet Media Types [17] in the Content-Type (section 14.17)
and Accept (section 14.1) header fields in order to provide
open and extensible data typing and type negotiation.

media-type     = type "/" subtype *( ";" parameter )
type           = token
subtype        = token
-
-   Parameters may
+   Parameters MAY
follow the type/subtype in the form of attribute/value
-   pairs.
+   pairs (as defined in section 3.6).
-
-          parameter      = attribute "=" value
-          attribute      = token
-          value          = token | quoted-string

    The type, subtype, and parameter attribute names are case-
-   insensitive.  Parameter values may or may not be case-sensitive,
+   insensitive. Parameter values might or might not be case-sensitive,
    depending on the semantics of the parameter name. Linear white space
    (LWS) MUST NOT be used between the type and subtype, nor between an
attribute and its value.
-   User agents that recognize the media-type MUST process (or arrange to be processed by any external applications
-   used to process that type/subtype by the user agent) the parameters
-   for that MIME type as described by that type/subtype definition to
-   the and inform the user of any problems discovered.
+   The presence or absence of a parameter might be significant to the processing of a media-type, depending on its
+   definition within the media type registry.
-
-     Note:
+   Note that
some older HTTP applications do not recognize media type
parameters. When sending data to older HTTP applications, implementations
-     should
+    SHOULD
only use media type parameters when they are
required by that type/subtype definition.
 
    Media-type values are registered with the Internet Assigned Number Authority
-   (IANA).
+   (IANA [19]).
The media type registration process is outlined in RFC
-   2048 [17].
+    [DEL[1590]] [INS[[INS[{errata}]] 2048]] [17].
Use of non-registered media types is discouraged.
 
 3.7.1 Canonicalization and Text Defaults
 
Internet media types are registered with a canonical form.
-   In general, an
+   An
entity-body transferred via HTTP messages MUST be represented in the appropriate canonical form prior to its transmission
-  ; the exception is
+   except for
"text" types, as defined in the next paragraph.
 
    When in canonical form, media subtypes of the "text" type use CRLF as
    the text line break. HTTP relaxes this requirement and allows the
@@ -1212,7 +1273,7 @@
    or LF MUST NOT be substituted for CRLF within any of the HTTP control
    structures (such as header fields and multipart boundaries).
 
-   If an entity-body is encoded with a Content-Encoding, the underlying
+   If an entity-body is encoded with a content-coding, the underlying
    data MUST be in a form defined above prior to being encoded.
 
    The "charset" parameter is used with some media types to define the
@@ -1220,83 +1281,83 @@
    parameter is provided by the sender, media subtypes of the "text"
    type are defined to have a default charset value of "ISO-8859-1" when
    received via HTTP. Data in character sets other than "ISO-8859-1" or
its subsets MUST be labeled with an appropriate charset value.
+   See section 3.4.1 for compatibility problems.
-
-   Some HTTP/1.0 software has interpreted a Content-Type header without
-   charset parameter incorrectly to mean "recipient should guess."
-   Senders wishing to defeat this behavior MAY include a charset
-   parameter even when the charset is ISO-8859-1 and SHOULD do so when
-   it is known that it will not confuse the recipient.
-
-   Unfortunately, some older HTTP/1.0 clients did not deal properly with
-   an explicit charset parameter. HTTP/1.1 recipients MUST respect the
-   charset label provided by the sender; and those user agents that have
-   a provision to "guess" a charset MUST use the charset from the
-   content-type field if they support that charset, rather than the
-   recipient's preference, when initially displaying a document.
 
 3.7.2 Multipart Types
 
    MIME provides for a number of "multipart" types -- encapsulations of
    one or more entities within a single message-body. All multipart
-   types share a common syntax, as defined in  MIME [7],
+   types share a common syntax, as defined in section 5.1.1 of RFC 2046 [40],
and MUST include a boundary parameter as part of the media type value. The
message body is itself a protocol element and MUST therefore use only
-   CRLF to represent line breaks between body-parts. Unlike in MIME, the
+   CRLF to represent line breaks between body-parts. Unlike in RFC 2046, the
epilogue of any multipart message MUST be empty; HTTP applications
MUST NOT transmit the epilogue (even if the original multipart
contains an epilogue).
+   These restrictions exist in
+   order to preserve the self-delimiting nature of a multipart message-
+   body, wherein the "end" of the message-body is indicated by the
+   ending multipart boundary.
-
-   In HTTP, multipart body-parts MAY contain header fields which are
-   significant to the meaning of that part. A Content-Location header
-   field (section 14.15) SHOULD be included in the body-part of each
-   enclosed entity that can be identified by a URL.

+   In general, HTTP treats a multipart message-body no differently than
+   any other media type: strictly as payload. The one exception is the
+   "multipart/byteranges" type (appendix 19.2) when it appears in a 206
+   (Partial Content) response, which will be interpreted by some HTTP
+   caching mechanisms as described in sections 13.5.4 and 14.16. In all
+   other cases, an HTTP user agent SHOULD follow the same or similar
+   behavior as a MIME user agent would upon receipt of a multipart type.
+   The MIME header fields within each body-part of a multipart message-
+   body do not have any significance to HTTP beyond that defined by
+   their MIME semantics.
 
    In general, an HTTP user agent SHOULD follow the same or similar
    behavior as a MIME user agent would upon receipt of a multipart type.
    If an application receives an unrecognized multipart subtype, the
    application MUST treat it as being equivalent to "multipart/mixed".
 
Note: The "multipart/form-data" type has been specifically defined
for carrying form data suitable for processing via the POST
request method, as described in RFC 1867 [15].
 
 3.8 Product Tokens
 
    Product tokens are used to allow communicating applications to
    identify themselves by software name and version. Most fields using
    product tokens also allow sub-products which form a significant part
-   of the application to be listed, separated by whitespace. By
+   of the application to be listed, separated by white space. By
    convention, the products are listed in order of their significance
    for identifying the application.
 
product         = token ["/" product-version]
product-version = token
 
    Examples:
 
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
Server: Apache/0.8.4
 
-   Product tokens should be short and to the point -- use of them
+   Product tokens SHOULD be short and to the point. They MUST NOT be used
for advertising or other non-essential information
-   is explicitly forbidden.  Although any token character may 
+  . Although any token character MAY
appear in a product-version, this token SHOULD only be used for a version identifier
(i.e., successive versions of the same product SHOULD only differ in
the product-version portion of the product value).
 
 3.9 Quality Values
 
    HTTP content negotiation (section 12) uses short "floating point"
    numbers to indicate the relative importance ("weight") of various
negotiable parameters.  A weight is normalized to a real number in the
range 0 through 1, where 0 is the minimum and 1 the maximum value.
+   If a parameter has a quality value of 0, then content with this parameter is `not acceptable' for the client.
HTTP/1.1 applications MUST NOT generate more than three digits after
the decimal point. User configuration of these values SHOULD also be
limited in this fashion.
 
qvalue         = ( "0" [ "." 0*3DIGIT ] ) | ( "1" [ "." 0*3("0") ] )
 
    "Quality values" is a misnomer, since these values merely represent
    relative degradation in desired quality.
@@ -1314,19 +1375,18 @@
3.10 Language Tags

   A language tag identifies a natural language spoken, written, or
   otherwise conveyed by human beings for communication of information
   to other human beings. Computer languages are explicitly excluded.
   HTTP uses language tags within the Accept-Language and Content-
   Language fields.

   The syntax and registry of HTTP language tags is the same as that
   defined by RFC 1766 [1]. In summary, a language tag is composed of 1
    or more parts: A primary language tag and a possibly empty series of
    subtags:
 
language-tag  = primary-tag *( "-" subtag )
primary-tag   = 1*8ALPHA
-           subtag        = 1*8ALPHA
+        subtag        = 1*8[DEL[ALPHA]] [INS[(ALPHA / DIGIT)]] [INS[{ammended by errata}]]
 
-
-   Whitespace is not allowed within the tag and all tags are case-
+   White space is not allowed within the tag and all tags are case-
    insensitive. The name space of language tags is administered by the
    IANA. Example tags include:
 
en, en-US, en-cockney, i-cherokee, x-pig-latin
 
-   where any two-letter primary-tag is an ISO 639 language abbreviation
+   where any two-letter primary-tag is an ISO-639 language abbreviation
-   and any two-letter initial subtag is an ISO 3166 country code. (The
+   and any two-letter initial subtag is an ISO-3166 country code. (The
    last three tags above are not registered tags; all but the last are
    examples of tags which could be registered in future.)
 
@@ -1334,45 +1394,46 @@
 
    Entity tags are used for comparing two or more entities from the same
    requested resource. HTTP/1.1 uses entity tags in the ETag (section
-   14.20), If-Match (section 14.25), If-None-Match (section 14.26), and
+   14.19), If-Match (section 14.24), If-None-Match (section 14.26), and
    If-Range (section 14.27) header fields. The definition of how they
    are used and compared as cache validators is in section 13.3.3. An
    entity tag consists of an opaque quoted string, possibly prefixed by
    a weakness indicator.
 
entity-tag = [ weak ] opaque-tag
weak       = "W/"
opaque-tag = quoted-string
 
-   A "strong entity tag" may be shared by two entities of a resource
+   A "strong entity tag" MAY be shared by two entities of a resource
    only if they are equivalent by octet equality.
 
-   A "weak entity tag," indicated by the "W/" prefix, may be shared by
+   A "weak entity tag," indicated by the "W/" prefix, MAY be shared by
    two entities of a resource only if the entities are equivalent and
    could be substituted for each other with no significant change in
    semantics. A weak entity tag can only be used for weak comparison.
 
    An entity tag MUST be unique across all versions of all entities
-   associated with a particular resource. A given entity tag value may
+   associated with a particular resource. A given entity tag value MAY
be used for entities obtained by requests on different URIs
-   without implying anything about the equivalence of those entities
.
+   The use of the same entity tag value in conjunction with entities obtained by
+   requests on different URIs does not imply the equivalence of those
+   entities.
 
 3.12 Range Units
 
    HTTP/1.1 allows a client to request that only part (a range of) the
    response entity be included within the response. HTTP/1.1 uses range
-   units in the Range (section 14.36) and Content-Range (section 14.17)
+   units in the Range (section 14.35) and Content-Range (section 14.16)
-   header fields. An entity may be broken down into subranges according
+   header fields. An entity can be broken down into subranges according
    to various structural units.
 
range-unit       = bytes-unit | other-range-unit
bytes-unit       = "bytes"
other-range-unit = token
 
 
The only range unit defined by HTTP/1.1 is "bytes". HTTP/1.1
-   implementations may ignore ranges specified using other units.
+   implementations MAY ignore ranges specified using other units.

    HTTP/1.1 has been designed to allow implementations of applications
    that do not depend on knowledge of ranges.
 
@@ -1383,31 +1444,30 @@
    HTTP messages consist of requests from client to server and responses
    from server to client.
 
HTTP-message   = Request | Response     ; HTTP/1.1 messages
 
    Request (section 5) and Response (section 6) messages use the generic
    message format of RFC 822 [9] for transferring entities (the payload
-   of the message). Both types of message consist of a start-line, one
+   of the message). Both types of message consist of a start-line, zero
    or more header fields (also known as "headers"), an empty line (i.e.,
    a line with nothing preceding the CRLF) indicating the end of the
-   header fields, and an optional message-body.
+   header fields, and possibly a message-body.
-
        generic-message = start-line
-                       *message-header
+                          *(message-header CRLF)
                          CRLF
                          [ message-body ]
 
start-line      = Request-Line | Status-Line
 
    In the interest of robustness, servers SHOULD ignore any empty
    line(s) received where a Request-Line is expected. In other words, if
    the server is reading the protocol stream at the beginning of a
    message and receives a CRLF first, it should ignore the CRLF.
 
-   Note: certain buggy HTTP/1.0 client implementations generate an
+         Certain buggy HTTP/1.0 client implementations generate
extra CRLF's after a POST request. To restate what is explicitly
-   forbidden by the BNF, an HTTP/1.1 client must not
+   forbidden by the BNF, an HTTP/1.1 client MUST NOT
preface or follow a request with an extra CRLF.
 
 4.2 Message Headers
 
@@ -1416,28 +1476,37 @@
    entity-header (section 7.1) fields, follow the same generic format as
    that given in Section 3.1 of RFC 822 [9]. Each header field consists
    of a name followed by a colon (":") and the field value. Field names
-   are case-insensitive. The field value may be preceded by any amount
+   are case-insensitive. The field value MAY be preceded by any amount
    of LWS, though a single SP is preferred. Header fields can be
    extended over multiple lines by preceding each extra line with at
-   least one SP or HT.  Applications SHOULD follow "common form"
+   least one SP or HT. Applications ought to follow "common form", where
+   one is known or indicated,
when generating HTTP constructs,
since there might exist some implementations that fail to accept anything
beyond the common forms.
-
-       message-header = field-name ":" [ field-value ] CRLF
+       message-header = field-name ":" [ field-value ]

field-name     = token
field-value    = *( field-content | LWS )

-field-content  = <the OCTETs making up the field-value and consisting of either *TEXT or combinations of token, tspecials, and quoted-string>
+field-content  = <the OCTETs making up the field-value and consisting of either *TEXT or combinations of token, separators, and quoted-string>
+
+   The field-content does not include any leading or trailing LWS:
+   linear white space occurring before the first non-whitespace
+   character of the field-value or after the last non-whitespace
+   character of the field-value. Such leading or trailing LWS MAY be
+   removed without changing the semantics of the field value. Any LWS
+   that occurs between field-content MAY be replaced with a single SP
+   before interpreting the field value or forwarding the message
+   downstream.
 
    The order in which header fields with differing field names are
    received is not significant. However, it is "good practice" to send
    general-header fields first, followed by request-header or response-
    header fields, and ending with the entity-header fields.
 
-   Multiple message-header fields with the same field-name may be
+   Multiple message-header fields with the same field-name MAY be
    present in a message if and only if the entire field-value for that
    header field is defined as a comma-separated list [i.e., #(values)].
    It MUST be possible to combine the multiple header fields into one
@@ -1448,32 +1517,36 @@
    interpretation of the combined field value, and thus a proxy MUST NOT
    change the order of these field values when a message is forwarded.
 
 4.3 Message Body
 
    The message-body (if any) of an HTTP message is used to carry the
    entity-body associated with the request or response. The message-body
-   differs from the entity-body only when a transfer coding has been
+   differs from the entity-body only when a transfer-coding has been
    applied, as indicated by the Transfer-Encoding header field (section
-   14.40).
+   14.41).

message-body = entity-body | <entity-body encoded as per Transfer-Encoding>
 
-   Transfer-Encoding MUST be used to indicate any transfer codings
+   Transfer-Encoding MUST be used to indicate any transfer-codings
    applied by an application to ensure safe and proper transfer of the
message. Transfer-Encoding is a property of the message, not of the
-   entity, and thus can be added or removed by any application along the
+   entity, and thus MAY be added or removed by any application along the
request/response chain.
+   (However, section 3.6 places restrictions on when certain transfer-codings may be used.)
 
    The rules for when a message-body is allowed in a message differ for
    requests and responses.
 
    The presence of a message-body in a request is signaled by the
    inclusion of a Content-Length or Transfer-Encoding header field in
-   the request's message-headers. A message-body MAY be included in a request
+   the request's message-headers. A message-body MUST NOT be included in a request
-   only when the request method (section 5.1.1) allows an entity-body.
+   if the specification of the request method (section 5.1.1)
+   does not allow sending an entity-body in requests. A server SHOULD
+   read and forward a message-body on any request; if the request method
+   does not include defined semantics for an entity-body, then the
+   message-body SHOULD be ignored when handling the request.
 
    For response messages, whether or not a message-body is included with
    a message is dependent on both the request method and the response
@@ -1482,35 +1555,50 @@
    header fields might lead one to believe they do. All 1xx
    (informational), 204 (no content), and 304 (not modified) responses
    MUST NOT include a message-body. All other responses do include a
-   message-body, although it may be of zero length.
+   message-body, although it MAY be of zero length.
 
 4.4 Message Length
 
+   The transfer-length of a message is the length of the message-body as
+   it appears in the message; that is, after any transfer-codings have been applied.
When a message-body is included with a message, the
-   length
+   transfer-length
of that body is determined by one of the following (in order of precedence):
 
-   1. Any response message which MUST NOT
+   1.Any response message which "MUST NOT"
include a message-body (such as the 1xx, 204, and 304 responses and any response to a HEAD
      request) is always terminated by the first empty line after the header fields, regardless of the entity-header fields present in the message.
-
-   2. If a Transfer-Encoding header field (section 14.40) is present and
+   2.If a Transfer-Encoding header field (section 14.41) is present [DEL[[INS[{removed by errata}]] and has any value other than "identity",]] then the transfer-length
-     indicates that the "chunked" transfer coding has been applied, then the length
 
-     is defined by the chunked encoding (section 3.6).
+     is defined by use of the "chunked" transfer-coding (section 3.6),
+     unless the message is terminated by closing the connection.
+
-   3. If a Content-Length header field (section 14.14) is present, its
+   3.If a Content-Length header field (section 14.13) is present, its
-     value in bytes represents the length of the message-body.
+     decimal value in OCTETs represents both the entity-length and the
+     transfer-length. The Content-Length header field MUST NOT be sent
+     if these two lengths are different (i.e., if a Transfer-Encoding
+     header field is present). If a message is received with both a
+     Transfer-Encoding header field and a Content-Length header field,
+     the latter MUST be ignored.
+
-   4. If the message uses the media type "multipart/byteranges", which is self-delimiting, then that
+   4.If the message uses the media type "multipart/byteranges", and the
+     [INS[t]]ransfer-length is not otherwise specified, then this self-[INS[d]]elimiting media type
-     defines the length. This media type MUST NOT
+      defines the transfer-length. This media type [INS[M]]UST NOT
-     be used unless the sender knows that the recipient can parse
+     be used unless the sender knows that the recipient can [INS[p]]arse
-     it; the presence in a request of a Range header with multiple
+     it; the presence in a request of a Range header with [INS[m]]ultiple 
-     byte-range specifiers implies that the client
+     byte-range specifiers from a 1.1 client implies that the [INS[c]]lient
can parse multipart/byteranges responses.
[INS[{ammended by errata}]]

+       A range header might be forwarded by a 1.0 proxy that does not
+       understand multipart/byteranges; in this case the server MUST
+       delimit the message using methods defined in items 1,3 or 5 of
+       this section.

5.By the server closing the connection. (Closing the connection
      cannot be used to indicate the end of a request body, since that
      would leave no possibility for the server to send back a response.)
 
@@ -1523,41 +1611,42 @@
    it wishes to insist on receiving a valid Content-Length.
 
    All HTTP/1.1 applications that receive entities MUST accept the
-   "chunked" transfer coding (section 3.6), thus allowing this mechanism
+   "chunked" transfer-coding (section 3.6), thus allowing this mechanism
    to be used for messages when the message length cannot be determined
    in advance.
 
Messages MUST NOT include both a Content-Length header field and
-   the "chunked" transfer coding. If both are received,
+   a [DEL[non-identity]] transfer-coding. If the message does include a [DEL[non-identity]] transfer-coding,
the Content-Length MUST be ignored.
[INS[{ammended by errata}]]
 
    When a Content-Length is given in a message where a message-body is
    allowed, its field value MUST exactly match the number of OCTETs in
    the message-body. HTTP/1.1 user agents MUST notify the user when an
    invalid length is received and detected.

 4.5 General Header Fields
 
    There are a few header fields which have general applicability for
    both request and response messages, but which do not apply to the
    entity being transferred. These header fields apply only to the
    message being transmitted.
 
-          general-header = Cache-Control            ; Section 14.9
-                         | Connection               ; Section 14.10
-                         | Date                     ; Section 14.19
-                         | Pragma                   ; Section 14.32
-                         | Transfer-Encoding        ; Section 14.40
-                         | Upgrade                  ; Section 14.41
-                         | Via                      ; Section 14.44
+       general-header = Cache-Control            ; Section 14.9
+                      | Connection               ; Section 14.10
+                      | Date                     ; Section 14.18
+                      | Pragma                   ; Section 14.32
+                      | Trailer                  ; Section 14.40
+                      | Transfer-Encoding        ; Section 14.41
+                      | Upgrade                  ; Section 14.42
+                      | Via                      ; Section 14.45
+                      | Warning                  ; Section 14.46
 
    General-header field names can be extended reliably only in
    combination with a change in the protocol version. However, new or
    experimental header fields may be given the semantics of general
    header fields if all parties in the communication recognize them to
be general-header fields. Unrecognized header fields are treated as
    entity-header fields.
 
 5 Request
@@ -1566,158 +1655,142 @@
    first line of that message, the method to be applied to the resource,
    the identifier of the resource, and the protocol version in use.
 
-           Request       = Request-Line              ; Section 5.1
-                           *( general-header         ; Section 4.5
-                            | request-header         ; Section 5.3
-                            | entity-header )        ; Section 7.1
-                           CRLF
-                           [ message-body ]          ; Section 7.2
+        Request       = Request-Line              ; Section 5.1
+                        *(( general-header        ; Section 4.5
+                         | request-header         ; Section 5.3
+                         | entity-header ) CRLF)  ; Section 7.1
+                        CRLF
+                        [ message-body ]          ; Section 4.3
 
 5.1 Request-Line
 
    The Request-Line begins with a method token, followed by the
    Request-URI and the protocol version, and ending with CRLF. The
-   elements are separated by SP characters. No CR or LF are allowed
+   elements are separated by SP characters. No CR or LF is allowed
    except in the final CRLF sequence.
 
Request-Line   = Method SP Request-URI SP HTTP-Version CRLF
 
 5.1.1 Method
 
The Method  token indicates the method to be performed on the
resource identified by the Request-URI. The method is case-sensitive.
 
-          Method         = "OPTIONS"                ; Section 9.2
-                         | "GET"                    ; Section 9.3
-                         | "HEAD"                   ; Section 9.4
-                         | "POST"                   ; Section 9.5
-                         | "PUT"                    ; Section 9.6
-                         | "DELETE"                 ; Section 9.7
-                         | "TRACE"                  ; Section 9.8
-                         | extension-method
-
+       Method         = "OPTIONS"                ; Section 9.2
+                      | "GET"                    ; Section 9.3
+                      | "HEAD"                   ; Section 9.4
+                      | "POST"                   ; Section 9.5
+                      | "PUT"                    ; Section 9.6
+                      | "DELETE"                 ; Section 9.7
+                      | "TRACE"                  ; Section 9.8
+                      | "CONNECT"                ; Section 9.9
+                      | extension-method
extension-method = token
 
    The list of methods allowed by a resource can be specified in an
    Allow header field (section 14.7). The return code of the response
    always notifies the client whether a method is currently allowed on a
resource, since the set of allowed methods can change dynamically.
-   Servers SHOULD return the status code 405 (Method Not Allowed)
+   An origin server SHOULD return the status code 405 (Method Not Allowed)
-   if the method is known by the server but not allowed for the
+   if the method is known by the origin server but not allowed for the
requested resource, and 501 (Not Implemented) if the method is unrecognized or
-   not implemented by the server.
+   not implemented by the origin server.
-   The list of methods known by a server can be listed in a Public response-header field (section 14.35).

The methods GET and HEAD MUST be supported by all general-purpose
-   servers. All other methods are optional; however, if the above
+   servers. All other methods are OPTIONAL; however, if the above
methods are implemented, they MUST be implemented with the same
semantics as those specified in section 9.

 5.1.2 Request-URI
 
    The Request-URI is a Uniform Resource Identifier (section 3.2) and
    identifies the resource upon which to apply the request.
 
-       Request-URI    = "*" | absoluteURI | abs_path
+       Request-URI    = "*" | absoluteURI | abs_path [INS[[INS[{errata}]] [ "?" query ] ]] | authority
 
-   The three options for Request-URI are dependent on the nature of the
+   The four options for Request-URI are dependent on the nature of the
    request. The asterisk "*" means that the request does not apply to a
    particular resource, but to the server itself, and is only allowed
    when the method used does not necessarily apply to a resource. One
    example would be
 
OPTIONS * HTTP/1.1
 
-   The absoluteURI form is required when the request is being made to a
+   The absoluteURI form is REQUIRED when the request is being made to a
    proxy. The proxy is requested to forward the request or service it
    from a valid cache, and return the response. Note that the proxy MAY
    forward the request on to another proxy or directly to the server
    specified by the absoluteURI. In order to avoid request loops, a
    proxy MUST be able to recognize all of its server names, including
    any aliases, local variations, and the numeric IP address. An example
    Request-Line would be:
 
GET http://www.w3.org/pub/WWW/TheProject.html HTTP/1.1
 
    To allow for transition to absoluteURIs in all requests in future
    versions of HTTP, all HTTP/1.1 servers MUST accept the absoluteURI
    form in requests, even though HTTP/1.1 clients will only generate
    them in requests to proxies.
 
+   The authority form is only used by the CONNECT method (section 9.9).

    The most common form of Request-URI is that used to identify a
    resource on an origin server or gateway. In this case the absolute
    path of the URI MUST be transmitted (see section 3.2.1, abs_path) as
-   the Request-URI, and the network location of the URI (net_loc) MUST
+   the Request-URI, and the network location of the URI (authority) MUST
    be transmitted in a Host header field. For example, a client wishing
    to retrieve the resource above directly from the origin server would
    create a TCP connection to port 80 of the host "www.w3.org" and send
    the lines:

GET /pub/WWW/TheProject.html HTTP/1.1
Host: www.w3.org
 
    followed by the remainder of the Request. Note that the absolute path
    cannot be empty; if none is present in the original URI, it MUST be
    given as "/" (the server root).
 
-   If a proxy receives a request without any path in the Request-URI and
-   the method specified is capable of supporting the asterisk form of
-   request, then the last proxy on the request chain MUST forward the
-   request with "*" as the final Request-URI. For example, the request
-
-          OPTIONS http://www.ics.uci.edu:8001 HTTP/1.1
-
-   would be forwarded by the proxy as
-
-          OPTIONS * HTTP/1.1
-          Host: www.ics.uci.edu:8001
-
-   after connecting to port 8001 of host "www.ics.uci.edu".
-
    The Request-URI is transmitted in the format specified in section 3.2.1.
+   If the Request-URI is encoded using the "% HEX HEX" encoding [42], the
-    The
origin server MUST decode the Request-URI in order to
    properly interpret the request. Servers SHOULD respond to invalid
    Request-URIs with an appropriate status code.
 
-   In requests that they forward, proxies MUST NOT rewrite the
-   "abs_path" part of a Request-URI in any way except as noted above to
-   replace a null abs_path with "*", no matter what the proxy does in
-   its internal implementation.
+   A transparent proxy MUST NOT rewrite the "abs_path" part of the
+   received Request-URI when forwarding it to the next inbound server,
+   except as noted above to replace a null abs_path with "/".

Note: The "no rewrite" rule prevents the proxy from changing the
meaning of the request when the origin server is improperly using a non-reserved
-      URL
+      URI
character for a reserved purpose.  Implementors
should be aware that some pre-HTTP/1.1 proxies have been known to rewrite the Request-URI.
 
 5.2 The Resource Identified by a Request
 
-   HTTP/1.1 origin servers SHOULD be aware that the
+   The
exact resource identified by an Internet request is determined by
examining both the Request-URI and the Host header field.
 
    An origin server that does not allow resources to differ by the
    requested host MAY ignore the Host header field value
+   when determining the resource identified by an HTTP/1.1 request
-  . (But see section 19.5.1
+  . (But see section 19.6.1.1
for other requirements on Host support in HTTP/1.1.)
 
    An origin server that does differentiate resources based on the host
    requested (sometimes referred to as virtual hosts or vanity
-   hostnames)
+   host names)
MUST use the following rules for determining the requested
    resource on an HTTP/1.1 request:

1. If Request-URI is an absoluteURI, the host is part of the
Request-URI. Any Host header field value in the request MUST be ignored.

2. If the Request-URI is not an absoluteURI, and the request
includes a Host header field, the host is determined by the Host header
field value.

3. If the host as determined by rule 1 or 2 is not a valid host on
the server, the response MUST be a 400 (Bad Request) error message.

    Recipients of an HTTP/1.0 request that lacks a Host header field MAY
    attempt to use heuristics (e.g., examination of the URI path for
@@ -1729,33 +1802,35 @@
    The request-header fields allow the client to pass additional
    information about the request, and about the client itself, to the
    server. These fields act as request modifiers, with semantics
    equivalent to the parameters on a programming language method
    invocation.
 
-          request-header = Accept                   ; Section 14.1
-                         | Accept-Charset           ; Section 14.2
-                         | Accept-Encoding          ; Section 14.3
-                         | Accept-Language          ; Section 14.4
-                         | Authorization            ; Section 14.8
-                         | From                     ; Section 14.22
-                         | Host                     ; Section 14.23
-                         | If-Modified-Since        ; Section 14.24
-                         | If-Match                 ; Section 14.25
-                         | If-None-Match            ; Section 14.26
-                         | If-Range                 ; Section 14.27
-                         | If-Unmodified-Since      ; Section 14.28
-                         | Max-Forwards             ; Section 14.31
-                         | Proxy-Authorization      ; Section 14.34
-                         | Range                    ; Section 14.36
-                         | Referer                  ; Section 14.37
-                         | User-Agent               ; Section 14.42
+       request-header = Accept                   ; Section 14.1
+                      | Accept-Charset           ; Section 14.2
+                      | Accept-Encoding          ; Section 14.3
+                      | Accept-Language          ; Section 14.4
+                      | Authorization            ; Section 14.8
+                      | Expect                   ; Section 14.20
+                      | From                     ; Section 14.22
+                      | Host                     ; Section 14.23
+                      | If-Match                 ; Section 14.24
+                      | If-Modified-Since        ; Section 14.25
+                      | If-None-Match            ; Section 14.26
+                      | If-Range                 ; Section 14.27
+                      | If-Unmodified-Since      ; Section 14.28
+                      | Max-Forwards             ; Section 14.31
+                      | Proxy-Authorization      ; Section 14.34
+                      | Range                    ; Section 14.35
+                      | Referer                  ; Section 14.36
+                      | TE                       ; Section 14.39
+                      | User-Agent               ; Section 14.43
 
    Request-header field names can be extended reliably only in
    combination with a change in the protocol version. However, new or
    experimental header fields MAY be given the semantics of request-
    header fields if all parties in the communication recognize them to
    be request-header fields. Unrecognized header fields are treated as
    entity-header fields.
 
 6 Response
@@ -1764,9 +1839,9 @@
    with an HTTP response message.
 
        Response      = Status-Line               ; Section 6.1
-                       *( general-header         ; Section 4.5
+                       *(( general-header        ; Section 4.5
                         | response-header        ; Section 6.2
-                        | entity-header )        ; Section 7.1
+                        | entity-header ) CRLF)  ; Section 7.1
                        CRLF
                        [ message-body ]          ; Section 7.2
 
@@ -1775,8 +1850,7 @@
    The first line of a Response message is the Status-Line, consisting
    of the protocol version followed by a numeric status code and its
    associated textual phrase, with each element separated by SP
    characters. No CR or LF is allowed except in the final CRLF sequence.
 
        Status-Line = HTTP-Version SP Status-Code SP Reason-Phrase CRLF
 
@@ -1794,69 +1868,72 @@
    last two digits do not have any categorization role. There are 5
    values for the first digit:
 
-     o  1xx: Informational - Request received, continuing process
+      - 1xx: Informational - Request received, continuing process
 
-     o  2xx: Success - The action was successfully received,
+      - 2xx: Success - The action was successfully received,
understood, and accepted
 
-     o  3xx: Redirection - Further action must be taken in order to
+      - 3xx: Redirection - Further action must be taken in order to
         complete the request
 
-     o  4xx: Client Error - The request contains bad syntax or cannot
+      - 4xx: Client Error - The request contains bad syntax or cannot
be fulfilled
 
-     o  5xx: Server Error - The server failed to fulfill an apparently
+      - 5xx: Server Error - The server failed to fulfill an apparently
         valid request
 
    The individual values of the numeric status codes defined for
    HTTP/1.1, and an example set of corresponding Reason-Phrase's, are
    presented below. The reason phrases listed here are only
-   recommended -- they may
+   recommendations -- they MAY
be replaced by local equivalents without affecting the protocol.
+
-          Status-Code    = "100"   ; Continue
-                         | "101"   ; Switching Protocols
-                         | "200"   ; OK
-                         | "201"   ; Created
-                         | "202"   ; Accepted
-                         | "203"   ; Non-Authoritative Information
-                         | "204"   ; No Content
-                         | "205"   ; Reset Content
-                         | "206"   ; Partial Content
-                         | "300"   ; Multiple Choices
-                         | "301"   ; Moved Permanently
-                         | "302"   ; Moved Temporarily
-                         | "303"   ; See Other
-                         | "304"   ; Not Modified
-                         | "305"   ; Use Proxy
-                         | "400"   ; Bad Request
-                         | "401"   ; Unauthorized
-                         | "402"   ; Payment Required
-                         | "403"   ; Forbidden
-                         | "404"   ; Not Found
-                         | "405"   ; Method Not Allowed
-                         | "406"   ; Not Acceptable
-                         | "407"   ; Proxy Authentication Required
-                         | "408"   ; Request Time-out
-                         | "409"   ; Conflict
-                         | "410"   ; Gone
-                         | "411"   ; Length Required
-                         | "412"   ; Precondition Failed
-                         | "413"   ; Request Entity Too Large
-                         | "414"   ; Request-URI Too Large
-                         | "415"   ; Unsupported Media Type
-                         | "500"   ; Internal Server Error
-                         | "501"   ; Not Implemented
-                         | "502"   ; Bad Gateway
-                         | "503"   ; Service Unavailable
-                         | "504"   ; Gateway Time-out
-                         | "505"   ; HTTP Version not supported
-                         | extension-code
-
+      Status-Code    =
+            "100"  ; Section 10.1.1: Continue
+          | "101"  ; Section 10.1.2: Switching Protocols
+          | "200"  ; Section 10.2.1: OK
+          | "201"  ; Section 10.2.2: Created
+          | "202"  ; Section 10.2.3: Accepted
+          | "203"  ; Section 10.2.4: Non-Authoritative Information
+          | "204"  ; Section 10.2.5: No Content
+          | "205"  ; Section 10.2.6: Reset Content
+          | "206"  ; Section 10.2.7: Partial Content
+          | "300"  ; Section 10.3.1: Multiple Choices
+          | "301"  ; Section 10.3.2: Moved Permanently
+          | "302"  ; Section 10.3.3: Found
+          | "303"  ; Section 10.3.4: See Other
+          | "304"  ; Section 10.3.5: Not Modified
+          | "305"  ; Section 10.3.6: Use Proxy
+          | "307"  ; Section 10.3.8: Temporary Redirect
+          | "400"  ; Section 10.4.1: Bad Request
+          | "401"  ; Section 10.4.2: Unauthorized
+          | "402"  ; Section 10.4.3: Payment Required
+          | "403"  ; Section 10.4.4: Forbidden
+          | "404"  ; Section 10.4.5: Not Found
+          | "405"  ; Section 10.4.6: Method Not Allowed
+          | "406"  ; Section 10.4.7: Not Acceptable
+          | "407"  ; Section 10.4.8: Proxy Authentication Required
+          | "408"  ; Section 10.4.9: Request Time-out
+          | "409"  ; Section 10.4.10: Conflict
+          | "410"  ; Section 10.4.11: Gone
+          | "411"  ; Section 10.4.12: Length Required
+          | "412"  ; Section 10.4.13: Precondition Failed
+          | "413"  ; Section 10.4.14: Request Entity Too Large
+          | "414"  ; Section 10.4.15: Request-URI Too Large
+          | "415"  ; Section 10.4.16: Unsupported Media Type
+          | "416"  ; Section 10.4.17: Requested range not satisfiable
+          | "417"  ; Section 10.4.18: Expectation Failed
+          | "500"  ; Section 10.5.1: Internal Server Error
+          | "501"  ; Section 10.5.2: Not Implemented
+          | "502"  ; Section 10.5.3: Bad Gateway
+          | "503"  ; Section 10.5.4: Service Unavailable
+          | "504"  ; Section 10.5.5: Gateway Time-out
+          | "505"  ; Section 10.5.6: HTTP Version not supported
+          | extension-code

extension-code = 3DIGIT
Reason-Phrase  = *<TEXT, excluding CR, LF>
 
    HTTP status codes are extensible. HTTP applications are not required
    to understand the meaning of all registered status codes, though such
@@ -1879,15 +1956,16 @@
    Line. These header fields give information about the server and about
    further access to the resource identified by the Request-URI.
 
-          response-header = Age                     ; Section 14.6
-                          | Location                ; Section 14.30
-                          | Proxy-Authenticate      ; Section 14.33
-                          | Public                  ; Section 14.35
-                          | Retry-After             ; Section 14.38
-                          | Server                  ; Section 14.39
-                          | Vary                    ; Section 14.43
-                          | Warning                 ; Section 14.45
-                          | WWW-Authenticate        ; Section 14.46
+       response-header = Accept-Ranges           ; Section 14.5
+                       | Age                     ; Section 14.6
+                       | ETag                    ; Section 14.19
+                       | Location                ; Section 14.30
+                       | Proxy-Authenticate      ; Section 14.33
+                       | Retry-After             ; Section 14.37
+                       | Server                  ; Section 14.38
+                       | Vary                    ; Section 14.44
+                       | WWW-Authenticate        ; Section 14.47
 
    Response-header field names can be extended reliably only in
    combination with a change in the protocol version. However, new or
@@ -1908,44 +1986,42 @@
 
 7.1 Entity Header Fields
 
-   Entity-header fields define optional
+   Entity-header fields define
metainformation about the entity-body or, if no body is present, about the resource identified by the request.

+   Some of this metainformation is OPTIONAL; some might be REQUIRED by
+   portions of this specification.
 
-          entity-header  = Allow                    ; Section 14.7
-                         | Content-Base             ; Section 14.11
-                         | Content-Encoding         ; Section 14.12
-                         | Content-Language         ; Section 14.13
-                         | Content-Length           ; Section 14.14
-                         | Content-Location         ; Section 14.15
-                         | Content-MD5              ; Section 14.16
-                         | Content-Range            ; Section 14.17
-                         | Content-Type             ; Section 14.18
-                         | ETag                     ; Section 14.20
-                         | Expires                  ; Section 14.21
-                         | Last-Modified            ; Section 14.29
-                         | extension-header
-
+       entity-header  = Allow                    ; Section 14.7
+                      | Content-Encoding         ; Section 14.11
+                      | Content-Language         ; Section 14.12
+                      | Content-Length           ; Section 14.13
+                      | Content-Location         ; Section 14.14
+                      | Content-MD5              ; Section 14.15
+                      | Content-Range            ; Section 14.16
+                      | Content-Type             ; Section 14.17
+                      | Expires                  ; Section 14.21
+                      | Last-Modified            ; Section 14.29
+                      | extension-header

extension-header = message-header
 
    The extension-header mechanism allows additional entity-header fields
    to be defined without changing the protocol, but these fields cannot
    be assumed to be recognizable by the recipient. Unrecognized header fields SHOULD be ignored by the recipient and
-   forwarded by proxies.
+   MUST be forwarded by transparent proxies.
 
 7.2 Entity Body
 
    The entity-body (if any) sent with an HTTP request or response is in
    a format and encoding defined by the entity-header fields.
    
    entity-body    = *OCTET
 
    An entity-body is only present in a message when a message-body is
    present, as described in section 4.3. The entity-body is obtained
    from the message-body by decoding any Transfer-Encoding that
-   may
+   might
have been applied to ensure safe and proper transfer of the message.
 
 7.2.1 Type
 
@@ -1953,7 +2029,7 @@
    body is determined via the header fields Content-Type and Content-
    Encoding. These define a two-layer, ordered encoding model:

entity-body := Content-Encoding( Content-Type( data ) )
 
    Content-Type specifies the media type of the underlying data.
    Content-Encoding may be used to indicate any additional content
@@ -1965,15 +2041,15 @@
    Content-Type header field defining the media type of that body. If
    and only if the media type is not given by a Content-Type field, the
    recipient MAY attempt to guess the media type via inspection of its
-   content and/or the name extension(s) of the URL used to identify the
+   content and/or the name extension(s) of the URI used to identify the
    resource. If the media type remains unknown, the recipient SHOULD
    treat it as type "application/octet-stream".
 
-7.2.2 Length
+7.2.2 Entity Length
 
-   The length of an entity-body is the length of the message-body after
+   The entity-length of a message is the length of the message-body before
-   any transfer codings have been removed. Section 4.4 defines
+   any transfer-codings have been applied. Section 4.4 defines
-   how the length of a message-body is determined.
+   how the transfer-length of a message-body is determined.
 
 8 Connections
 
@@ -1984,27 +2060,38 @@
    Prior to persistent connections, a separate TCP connection was
    established to fetch each URL, increasing the load on HTTP servers
    and causing congestion on the Internet. The use of inline images and
-   other associated data often requires a client to make multiple
+   other associated data often require a client to make multiple
requests of the same server in a short amount of time. Analysis of
-   these performance problems are available [30][27]; analysis and
+   these performance problems and
-   results from a prototype implementation are in [26].
+   results from a prototype implementation are available [26] [30].
+   Implementation experience and measurements of actual HTTP/1.1 (RFC 2068) implementations show good
+   results [39]. Alternatives have also been explored, for example,
+   T/TCP [27].
 
    Persistent HTTP connections have a number of advantages:
 
-     o  By opening and closing fewer TCP connections, CPU time is saved,
+      - By opening and closing fewer TCP connections, CPU time is saved
+        in routers and hosts (clients, servers, proxies, gateways,
+        tunnels, or caches),
-        and memory used for TCP protocol control blocks is also saved.
+        and memory used for TCP protocol control blocks can be saved in hosts.
-     o  HTTP requests and responses can be pipelined on a connection.
+      - HTTP requests and responses can be pipelined on a connection.
         Pipelining allows a client to make multiple requests without
waiting for each response, allowing a single TCP connection to be
used much more efficiently, with much lower elapsed time.
-     o  Network congestion is reduced by reducing the number of packets
+      - Network congestion is reduced by reducing the number of packets
         caused by TCP opens, and by allowing TCP sufficient time to
         determine the congestion state of the network.
+      - Latency on subsequent requests is reduced since there is no time
+        spent in TCP's connection opening handshake.
-     o  HTTP can evolve more gracefully; since errors can be reported
+      - HTTP can evolve more gracefully, since errors can be reported
         without the penalty of closing the TCP connection. Clients using
future versions of HTTP might optimistically try a new feature,
but if communicating with an older server, retry with old semantics
after an error is reported.
 
    HTTP implementations SHOULD implement persistent connections.
 
@@ -2012,13 +2099,14 @@
 
    A significant difference between HTTP/1.1 and earlier versions of
    HTTP is that persistent connections are the default behavior of any
HTTP connection. That is, unless otherwise indicated, the client
-   may assume that the server will maintain a persistent connection.
+   SHOULD assume that the server will maintain a persistent connection,
+   even after error responses from the server.
 
    Persistent connections provide a mechanism by which a client and a
    server can signal the close of a TCP connection. This signaling takes
-   place using the Connection header field.
+   place using the Connection header field (section 14.10).
-   Once a close has been signaled, the client MUST not
+   Once a close has been signaled, the client MUST NOT 
send any more requests on that    connection.
 
 8.1.2.1 Negotiation
@@ -2043,10 +2131,10 @@
 
    Clients and servers SHOULD NOT assume that a persistent connection is
    maintained for HTTP versions less than 1.1 unless it is explicitly
-   signaled. See section 19.7.1 for more information on backwards
+   signaled. See section 19.6.2 for more information on backward
    compatibility with HTTP/1.0 clients.
 
-   In order to remain persistent, all messages on the connection must
+   In order to remain persistent, all messages on the connection MUST
    have a self-defined message length (i.e., one not defined by closure
    of the connection), as described in section 4.4.
 
@@ -2065,18 +2153,28 @@
    the server closes the connection before sending all of the
    corresponding responses.
 
+   Clients SHOULD NOT pipeline requests using non-idempotent methods or
+   non-idempotent sequences of methods (see section 9.1.2). Otherwise, a
+   premature termination of the transport connection could lead to
+   indeterminate results. A client wishing to send a non-idempotent
+   request SHOULD wait to send that request until it has received the
+   response status for the previous request.
+
 8.1.3 Proxy Servers
 
    It is especially important that proxies correctly implement the
-   properties of the Connection header field as specified in 14.2.1.
+   properties of the Connection header field as specified in section
+   14.10.
 
    The proxy server MUST signal persistent connections separately with
    its clients and the origin servers (or other proxy servers) that it
    connects to. Each persistent connection applies to only one transport
    link.
 
-   A proxy server MUST NOT establish a
+   A proxy server MUST NOT establish a HTTP/1.1
-   persistent connection with an HTTP/1.0 client.
+   persistent connection with an HTTP/1.0 client
+   (but see RFC 2068 [33] for information and discussion of the problems with the Keep-Alive header implemented by many HTTP/1.0 clients).
 
 8.1.4 Practical Considerations
 
@@ -2084,8 +2182,8 @@
    no longer maintain an inactive connection. Proxy servers might make
    this a higher value since it is likely that the client will be making
    more connections through the same server. The use of persistent
-   connections places no requirements on the length
+   connections places no requirements on the length (or existence)
of this time-out for either the client or the server.
 
    When a client or server wishes to time-out it SHOULD issue a graceful
    close on the transport connection. Clients and servers SHOULD both
@@ -2095,23 +2193,22 @@
    drain on the network.
 
    A client, server, or proxy MAY close the transport connection at any
-   time. For example, a client MAY
+   time. For example, a client might
have started to send a new request at the same time that the server has decided to close the "idle"
    connection. From the server's point of view, the connection is being
    closed while it was idle, but from the client's point of view, a
    request is in progress.
 
    This means that clients, servers, and proxies MUST be able to recover
    from asynchronous close events. Client software SHOULD reopen the
-   transport connection and retransmit the aborted request
+   transport connection and retransmit the aborted sequence of requests
-   without user interaction so long as the request method is
+   without user interaction so long as the request sequence is
-   idempotent (see section 9.1.2); other methods
+   idempotent (see section 9.1.2). Non-idempotent methods or sequences
MUST NOT be automatically retried, although user agents MAY offer
-   a human operator the choice of retrying the request. However, this
+   a human operator the choice of retrying the request(s). Confirmation by
+   user-agent software with semantic understanding of the application
+   MAY substitute for user confirmation. The
automatic retry SHOULD NOT be repeated if the second
-   request fails.
+   sequence of requests fails.
 
    Servers SHOULD always respond to at least one request per connection,
    if at all possible. Servers SHOULD NOT close a connection in the
@@ -2120,108 +2217,170 @@
 
    Clients that use persistent connections SHOULD limit the number of
    simultaneous connections that they maintain to a given server. A
-   single-user client SHOULD maintain AT MOST
+   single-user client SHOULD NOT maintain more than
2 connections with any server or proxy. A proxy SHOULD use up to 2*N connections to another
server or proxy, where N is the number of simultaneously active
users. These guidelines are intended to improve HTTP response times and avoid congestion
-   of the Internet or other networks.
+  .
 
 8.2 Message Transmission Requirements
 
-General requirements:
+8.2.1 Persistent Connections and Flow Control
+
-o  HTTP/1.1 servers SHOULD maintain persistent connections and use
+   HTTP/1.1 servers SHOULD maintain persistent connections and use
TCP's flow control mechanisms to resolve temporary overloads,
rather than terminating connections with the expectation that clients will retry.
The latter technique can exacerbate network congestion.
 
+8.2.2 Monitoring Connections for Error Status Messages
 
-o  An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
+   An HTTP/1.1 (or later) client sending a message-body SHOULD monitor
    the network connection for an error status while it is transmitting
    the request. If the client sees an error status, it SHOULD
    immediately cease transmitting the body. If the body is being sent
    using a "chunked" encoding (section 3.6), a zero length chunk and
-   empty footer
+   empty trailer
MAY be used to prematurely mark the end of the message. If the body was preceded by a Content-Length header, the client MUST close the connection.
-
-o  An HTTP/1.1 (or later) client MUST be prepared to accept a 100
-   (Continue) status followed by a regular response.
-
-o  An HTTP/1.1 (or later) server that receives a request from a
-   HTTP/1.0 (or earlier) client MUST NOT transmit the 100 (continue)
-   response; it SHOULD either wait for the request to be completed
-   normally (thus avoiding an interrupted request) or close the
-   connection prematurely.
-
-   Upon receiving a method subject to these requirements from an
-   HTTP/1.1 (or later) client, an HTTP/1.1 (or later) server MUST either
-   respond with 100 (Continue) status and continue to read from the
-   input stream, or respond with an error status. If it responds with an
-   error status, it MAY close the transport (TCP) connection or it MAY
-   continue to read and discard the rest of the request. It MUST NOT
-   perform the requested method if it returns an error status.
-
-   Clients SHOULD remember the version number of at least the most
-   recently used server; if an HTTP/1.1 client has seen an HTTP/1.1 or
-   later response from the server, and it sees the connection close
-   before receiving any status from the server, the client SHOULD retry
-   the request without user interaction so long as the request method is
-   idempotent (see section 9.1.2); other methods MUST NOT be
-   automatically retried, although user agents MAY offer a human
-   operator the choice of retrying the request.. If the client does
-   retry the request, the client
-
-     o  MUST first send the request header fields, and then
-
-     o  MUST wait for the server to respond with either a 100 (Continue)
-        response, in which case the client should continue, or with an
-        error status.
-
-   If an HTTP/1.1 client has not seen an HTTP/1.1 or later response from
-   the server, it should assume that the server implements HTTP/1.0 or
-   older and will not use the 100 (Continue) response. If in this case
-   the client sees the connection close before receiving any status from
-   the server, the client SHOULD retry the request. If the client does
-   retry the request to this HTTP/1.0 server, it should use the
-   following "binary exponential backoff" algorithm to be assured of
-   obtaining a reliable response:
-
-  1. Initiate a new connection to the server
-
-  2. Transmit the request-headers
-
-  3. Initialize a variable R to the estimated round-trip time to the
-     server (e.g., based on the time it took to establish the
-     connection), or to a constant value of 5 seconds if the round-trip
-     time is not available.
-
-  4. Compute T = R * (2**N), where N is the number of previous retries
-     of this request.
-
-  5. Wait either for an error response from the server, or for T seconds
-     (whichever comes first)
-
-  6. If no error response is received, after T seconds transmit the body
-     of the request.
-
-  7. If client sees that the connection is closed prematurely, repeat
-     from step 1 until the request is accepted, an error response is
-     received, or the user becomes impatient and terminates the retry
-     process.
-
-   No matter what the server version, if an error status is received,
-   the client
-
-  o  MUST NOT continue and
-
-  o  MUST close the connection if it has not completed sending the
-     message.
-
-   An HTTP/1.1 (or later) client that sees the connection close after
-   receiving a 100 (Continue) but before receiving any other status
-   SHOULD retry the request, and need not wait for 100 (Continue)
-   response (but MAY do so if this simplifies the implementation).
+
+8.2.3 Use of the 100 (Continue) Status
+
+   The purpose of the 100 (Continue) status (see section 10.1.1) is to
+   allow a client that is sending a request message with a request body
+   to determine if the origin server is willing to accept the request
+   (based on the request headers) before the client sends the request
+   body. In some cases, it might either be inappropriate or highly
+   inefficient for the client to send the body if the server will reject
+   the message without looking at the body.
+
+   Requirements for HTTP/1.1 clients:
+
+      - If a client will wait for a 100 (Continue) response before
+        sending the request body, it MUST send an Expect request-header
+        field (section 14.20) with the "100-continue" expectation.
+
+      - A client MUST NOT send an Expect request-header field (section
+        14.20) with the "100-continue" expectation if it does not intend
+        to send a request body.
+
+   Because of the presence of older implementations, the protocol allows
+   ambiguous situations in which a client may send "Expect: 100-
+   continue" without receiving either a 417 (Expectation Failed) status
+   or a 100 (Continue) status. Therefore, when a client sends this
+   header field to an origin server (possibly via a proxy) from which it
+   has never seen a 100 (Continue) status, the client SHOULD NOT wait
+   for an indefinite period before sending the request body.
+
+   Requirements for HTTP/1.1 origin servers:
+
+      - Upon receiving a request which includes an Expect request-header
+        field with the "100-continue" expectation, an origin server MUST
+        either respond with 100 (Continue) status and continue to read
+        from the input stream, or respond with a final status code. The
+        origin server MUST NOT wait for the request body before sending
+        the 100 (Continue) response. If it responds with a final status
+        code, it MAY close the transport connection or it MAY continue
+
+        to read and discard the rest of the request.  It MUST NOT
+        perform the requested method if it returns a final status code.
+
+      - An origin server SHOULD NOT send a 100 (Continue) response if
+        the request message does not include an Expect request-header
+        field with the "100-continue" expectation, and MUST NOT send a
+        100 (Continue) response if such a request comes from an HTTP/1.0
+        (or earlier) client. There is an exception to this rule: for
+        compatibility with RFC 2068, a server MAY send a 100 (Continue)
+        status in response to an HTTP/1.1 PUT or POST request that does
+        not include an Expect request-header field with the "100-
+        continue" expectation. This exception, the purpose of which is
+        to minimize any client processing delays associated with an
+        undeclared wait for 100 (Continue) status, applies only to
+        HTTP/1.1 requests, and not to requests with any other HTTP-
+        version value.
+
+      - An origin server MAY omit a 100 (Continue) response if it has
+        already received some or all of the request body for the
+        corresponding request.
+
+      - An origin server that sends a 100 (Continue) response MUST
+        ultimately send a final status code, once the request body is
+        received and processed, unless it terminates the transport
+        connection prematurely.
+
+      - If an origin server receives a request that does not include an
+        Expect request-header field with the "100-continue" expectation,
+        the request includes a request body, and the server responds
+        with a final status code before reading the entire request body
+        from the transport connection, then the server SHOULD NOT close
+        the transport connection until it has read the entire request,
+        or until the client closes the connection. Otherwise, the client
+        might not reliably receive the response message. However, this
+        requirement is not be construed as preventing a server from
+        defending itself against denial-of-service attacks, or from
+        badly broken client implementations.
+
+   Requirements for HTTP/1.1 proxies:
+
+      - If a proxy receives a request that includes an Expect request-
+        header field with the "100-continue" expectation, and the proxy
+        either knows that the next-hop server complies with HTTP/1.1 or
+        higher, or does not know the HTTP version of the next-hop
+        server, it MUST forward the request, including the Expect header
+        field.
+
+      - If the proxy knows that the version of the next-hop server is
+        HTTP/1.0 or lower, it MUST NOT forward the request, and it MUST
+        respond with a 417 (Expectation Failed) status.
+
+      - Proxies SHOULD maintain a cache recording the HTTP version
+        numbers received from recently-referenced next-hop servers.
+
+      - A proxy MUST NOT forward a 100 (Continue) response if the
+        request message was received from an HTTP/1.0 (or earlier)
+        client and did not include an Expect request-header field with
+        the "100-continue" expectation. This requirement overrides the
+        general rule for forwarding of 1xx responses (see section 10.1).
+
+8.2.4 Client Behavior if Server Prematurely Closes Connection
+
+   If an HTTP/1.1 client sends a request which includes a request body,
+   but which does not include an Expect request-header field with the
+   "100-continue" expectation, and if the client is not directly
+   connected to an HTTP/1.1 origin server, and if the client sees the
+   connection close before receiving any status from the server, the
+   client SHOULD retry the request.  If the client does retry this
+   request, it MAY use the following "binary exponential backoff"
+   algorithm to be assured of obtaining a reliable response:
+
+      1. Initiate a new connection to the server
+
+      2. Transmit the request-headers
+
+      3. Initialize a variable R to the estimated round-trip time to the
+         server (e.g., based on the time it took to establish the
+         connection), or to a constant value of 5 seconds if the round-
+         trip time is not available.
+
+      4. Compute T = R * (2**N), where N is the number of previous
+         retries of this request.
+
+      5. Wait either for an error response from the server, or for T
+         seconds (whichever comes first)
+
+      6. If no error response is received, after T seconds transmit the
+         body of the request.
+
+      7. If client sees that the connection is closed prematurely,
+         repeat from step 1 until the request is accepted, an error
+         response is received, or the user becomes impatient and
+         terminates the retry process.
+
+   If at any point an error status is received, the client
+
+      - SHOULD NOT continue and
+
+      - SHOULD close the connection if it has not completed sending the
+        request message.
 
 9 Method Definitions
 
@@ -2236,31 +2395,43 @@
 
 9.1.1 Safe Methods
 
-   Implementers should be aware that the software represents the user in
+   Implementors should be aware that the software represents the user in
    their interactions over the Internet, and should be careful to allow
-   the user to be aware of any actions they may take which may have an
+   the user to be aware of any actions they might take which may have an
    unexpected significance to themselves or others.
 
    In particular, the convention has been established that the GET and
-   HEAD methods should never have the significance of taking an action
+   HEAD methods SHOULD NOT have the significance of taking an action
-   other than retrieval. These methods should be considered "safe."
+   other than retrieval. These methods ought to be considered "safe".
This allows user agents to represent other methods, such as POST, PUT
and DELETE, in a special way, so that the user is made aware of the
fact that a possibly unsafe action is being requested.
 
    Naturally, it is not possible to ensure that the server does not
    generate side-effects as a result of performing a GET request; in
    fact, some dynamic resources consider that a feature. The important
    distinction here is that the user did not request the side-effects,
    so therefore cannot be held accountable for them.
 
 9.1.2 Idempotent Methods
 
-   Methods may also have the property of "idempotence" in that (aside
+   Methods can also have the property of "idempotence" in that (aside
from error or expiration issues) the side-effects of N > 0 identical
    requests is the same as for a single request. The methods GET, HEAD,
    PUT and DELETE share this property.
+   Also, the methods OPTIONS and TRACE SHOULD NOT have side effects, and so are inherently idempotent.
+
+   However, it is possible that a sequence of several requests is non-
+   idempotent, even if all of the methods executed in that sequence are
+   idempotent. (A sequence is idempotent if a single execution of the
+   entire sequence always yields a result that is not changed by a
+   reexecution of all, or part, of that sequence.) For example, a
+   sequence is non-idempotent if its result depends on a value that is
+   later modified in the same sequence.
+
+   A sequence that never has side effects is idempotent, by definition
+   (provided that no concurrent operations are being executed on the
+   same set of resources).
 
 9.2 OPTIONS
 
@@ -2271,30 +2442,50 @@
    or the capabilities of a server, without implying a resource action
    or initiating a resource retrieval.
 
-   Unless the server's response is an error, the response MUST NOT
-   include entity information other than what can be considered as
-   communication options (e.g., Allow is appropriate, but Content-Type is not).
-   Responses to this method are not cachable.
+   Responses to this method are not cacheable.
+
+   If the OPTIONS request includes an entity-body (as indicated by the
+   presence of Content-Length or Transfer-Encoding), then the media type
+   MUST be indicated by a Content-Type field. Although this
+   specification does not define any use for such a body, future
+   extensions to HTTP might use the OPTIONS body to make more detailed
+   queries on the server. A server that does not support such an
+   extension MAY discard the request body.
 
    If the Request-URI is an asterisk ("*"), the OPTIONS request is
-   intended to apply to the server as a whole. A 200 response SHOULD
+   intended to apply to the server in general rather than to a specific resource.
-   include any header fields which indicate optional features
-   implemented by the server (e.g., Public), including any extensions
-   not defined by this specification, in addition to any applicable
-   general or response-header fields. As described in section 5.1.2, an
-   "OPTIONS *" request can be applied through a proxy by specifying the
-   destination server in the Request-URI without any path information.
+   Since a server's communication options typically depend on
+   the resource, the "*" request is only useful as a "ping" or "no-op"
+   type of method; it does nothing beyond allowing the client to test
+   the capabilities of the server. For example, this can be used to test
+   a proxy for HTTP/1.1 compliance (or lack thereof).
 
    If the Request-URI is not an asterisk, the OPTIONS request applies
    only to the options that are available when communicating with that resource.

A 200 response SHOULD include any header fields that indicate
optional features implemented by the server and applicable to that resource (e.g., Allow),
-   including any extensions not defined by this specification,
+   possibly including extensions not defined by this specification.
-   in addition to any applicable general or response-header fields.
-   If the OPTIONS request passes through a proxy, the proxy MUST edit the response to exclude those options
-   which apply to a proxy's capabilities and which are known to be
-   unavailable through that proxy.
+   The response body, if any, SHOULD also include
+   information about the communication options. The format for such a
+   body is not defined by this specification, but might be defined by
+   future extensions to HTTP. Content negotiation MAY be used to select
+   the appropriate response format. If no response body is included, the
+   response MUST include a Content-Length field with a field-value of
+   "0".
+
+   The Max-Forwards request-header field MAY be used to target a
+   specific proxy in the request chain. When a proxy receives an OPTIONS
+   request on an absoluteURI for which request forwarding is permitted,
+   the proxy MUST check for a Max-Forwards field. If the Max-Forwards
+   field-value is zero ("0"), the proxy MUST NOT forward the message;
+   instead, the proxy SHOULD respond with its own communication options.
+   If the Max-Forwards field-value is an integer greater than zero, the
+   proxy MUST decrement the field-value when it forwards the request. If
+   no Max-Forwards field is present in the request, then the forwarded
+   request MUST NOT include a Max-Forwards field.
 
 9.3 GET
 
@@ -2316,12 +2507,14 @@
    The semantics of the GET method change to a "partial GET" if the
    request message includes a Range header field. A partial GET requests
    that only part of the entity be transferred, as described in section
-   14.36. The partial GET method is intended to reduce unnecessary
+   14.35. The partial GET method is intended to reduce unnecessary
    network usage by allowing partially-retrieved entities to be
    completed without transferring data already held by the client.
 
-   The response to a GET request is cachable
+   The response to a GET request is cacheable
if and only if it meets the requirements for HTTP caching described in section 13.
+
+   See section 15.1.3 for security considerations when used for forms.
 
 9.4 HEAD
 
@@ -2334,8 +2527,8 @@
    often used for testing hypertext links for validity, accessibility,
    and recent modification.
 
-   The response to a HEAD request may be cachable in the sense that the
+   The response to a HEAD request MAY be cacheable in the sense that the
-   information contained in the response may be used to update a
+   information contained in the response MAY be used to update a
    previously cached entity from that resource. If the new field values
    indicate that the cached entity differs from the current entity (as
    would be indicated by a change in Content-Length, Content-MD5, ETag
@@ -2344,20 +2537,20 @@
 
 9.5 POST
 
-   The POST method is used to request that the destination
+   The POST method is used to request that the origin
-   server accept the entity enclosed in the request as a new subordinate of
+   server accept the entity enclosed in the request as [DEL[a new subordinate of]] [INS[{errata}]] [INS[data to be processed by]]
the resource identified by the Request-URI in the Request-Line. POST is
designed to allow a uniform method to cover the following functions:
 
-     o  Annotation of existing resources;
+      - Annotation of existing resources;
 
-     o  Posting a message to a bulletin board, newsgroup, mailing list,
+      - Posting a message to a bulletin board, newsgroup, mailing list,
         or similar group of articles;
 
-     o  Providing a block of data, such as the result of submitting a
+      - Providing a block of data, such as the result of submitting a
         form, to a data-handling process;
 
-     o  Extending a database through an append operation.
+      - Extending a database through an append operation.
 
    The actual function performed by the POST method is determined by the
    server and is usually dependent on the Request-URI. [DEL[The posted entity
   is subordinate to that URI in the same way that a file is subordinate
   to a directory containing it, a news article is subordinate to a
   newsgroup to which it is posted, or a record is subordinate to a
   database. [INS[{removed by errata}]]]]

   The action performed by the POST method might not result in a
   resource that can be identified by a URI. In this case, either 200
   (OK) or 204 (No Content) is the appropriate response status,
   depending on whether or not the response includes an entity that
   describes the result.

   If a resource has been created on the origin server, the response
   SHOULD be 201 (Created) and contain an entity which describes the
    status of the request and refers to the new resource, and a Location
    header (see section 14.30).
 
-   Responses to this method are not cachable, unless the response
+   Responses to this method are not cacheable, unless the response
    includes appropriate Cache-Control or Expires header fields. However,
    the 303 (See Other) response can be used to direct the user agent to
-   retrieve a cachable resource.
+   retrieve a cacheable resource.
 
-   POST requests must obey the message transmission requirements set out
+   POST requests MUST obey the message transmission requirements set out
    in section 8.2.
 
+   See section 15.1.3 for security considerations.
 
 9.6 PUT
 
@@ -2396,7 +2590,7 @@
    capable of being defined as a new resource by the requesting user
    agent, the origin server can create the resource with that URI. If a
    new resource is created, the origin server MUST inform the user agent
-   via the 201 (Created) response.  If an existing resource is modified,
+   via the 201 (Created) response. If an existing resource is modified,
    either the 200 (OK) or 204 (No Content) response codes SHOULD be sent
    to indicate successful completion of the request. If the resource
    could not be created or modified with the Request-URI, an appropriate
@@ -2406,34 +2600,39 @@
    and MUST return a 501 (Not Implemented) response in such cases.
 
    If the request passes through a cache and the Request-URI identifies
-   one or more currently cached entities, those entries should be
+   one or more currently cached entities, those entries SHOULD be
-   treated as stale. Responses to this method are not cachable.
+   treated as stale. Responses to this method are not cacheable.
 
    The fundamental difference between the POST and PUT requests is
    reflected in the different meaning of the Request-URI. The URI in a
    POST request identifies the resource that will handle the enclosed
-   entity.  That resource may be a data-accepting process, a gateway to
+   entity. That resource might be a data-accepting process, a gateway to
    some other protocol, or a separate entity that accepts annotations.
    In contrast, the URI in a PUT request identifies the entity enclosed
    with the request -- the user agent knows what URI is intended and the
    server MUST NOT attempt to apply the request to some other resource.
    If the server desires that the request be applied to a different URI,
    it MUST send a 301 (Moved Permanently) response; the user agent MAY
    then make its own decision regarding whether or not to redirect the
    request.
 
    A single resource MAY be identified by many different URIs. For
-   example, an article may have a URI for identifying "the current
+   example, an article might have a URI for identifying "the current
    version" which is separate from the URI identifying each particular
-   version. In this case, a PUT request on a general URI may result in
+   version. In this case, a PUT request on a general URI might result in
    several other URIs being defined by the origin server.
 
    HTTP/1.1 does not define how a PUT method affects the state of an
    origin server.
 
-   PUT requests must obey the message transmission requirements set out
+   PUT requests MUST obey the message transmission requirements set out
    in section 8.2.
 
+   Unless otherwise specified for a particular entity-header, the
+   entity-headers in the PUT request SHOULD be applied to the resource
+   created or modified by the PUT.
+
 9.7 DELETE
 
    The DELETE method requests that the origin server delete the resource
@@ -2441,19 +2640,19 @@
    intervention (or other means) on the origin server. The client cannot
    be guaranteed that the operation has been carried out, even if the
    status code returned from the origin server indicates that the action
-   has been completed successfully. However, the server SHOULD not
+   has been completed successfully. However, the server SHOULD NOT
    indicate success unless, at the time the response is given, it
    intends to delete the resource or move it to an inaccessible
    location.
 
    A successful response SHOULD be 200 (OK) if the response includes an
    entity describing the status, 202 (Accepted) if the action has not yet been enacted, or 204 (No Content) if the
-   response is OK but
+   action has been enacted but the response
does not include an entity.
 
    If the request passes through a cache and the Request-URI identifies
-   one or more currently cached entities, those entries should be
+   one or more currently cached entities, those entries SHOULD be
-   treated as stale. Responses to this method are not cachable.
+   treated as stale. Responses to this method are not cacheable.
 
 9.8 TRACE
 
@@ -2461,21 +2660,28 @@
    back of the request message. The final recipient of the request
    SHOULD reflect the message received back to the client as the
    entity-body of a 200 (OK) response. The final recipient is either the
    origin server or the first proxy or gateway to receive a Max-Forwards
    value of zero (0) in the request (see section 14.31). A TRACE request
    MUST NOT include an entity.
 
    TRACE allows the client to see what is being received at the other
    end of the request chain and use that data for testing or diagnostic
-   information. The value of the Via header field (section 14.44) is of
+   information. The value of the Via header field (section 14.45) is of
    particular interest, since it acts as a trace of the request chain.
    Use of the Max-Forwards header field allows the client to limit the
    length of the request chain, which is useful for testing a chain of
    proxies forwarding messages in an infinite loop.
 
-   If successful, the response SHOULD
+   If the request is valid, the response SHOULD
contain the entire request message in the entity-body, with a Content-Type of
"message/http". Responses to this method MUST NOT be cached.
+
+9.9 CONNECT
+
+   This specification reserves the method name CONNECT for use with a
+   proxy that can dynamically switch to being a tunnel (e.g. SSL
+   tunneling [44]).
 
 10 Status Code Definitions
 
@@ -2487,33 +2693,49 @@
 
    This class of status code indicates a provisional response,
    consisting only of the Status-Line and optional headers, and is
terminated by an empty line.
+ There are no required headers for this class of status code.
Since HTTP/1.0 did not define any 1xx status codes, servers MUST NOT send
a 1xx response to an HTTP/1.0 client except under experimental conditions.
+
+   A client MUST be prepared to accept one or more 1xx status responses
+   prior to a regular response, even if the client does not expect a 100
+   (Continue) status message. Unexpected 1xx status responses MAY be
+   ignored by a user agent.
+
+   Proxies MUST forward 1xx responses, unless the connection between the
+   proxy and its client has been closed, or unless the proxy itself
+   requested the generation of the 1xx response. (For example, if a
+   proxy adds a "Expect: 100-continue" field when it forwards a request,
+   then it need not forward the corresponding 100 (Continue)
+   response(s).)
 
 10.1.1 100 Continue
 
-   The client may continue with its request. This interim response is
+   The client SHOULD continue with its request. This interim response is
    used to inform the client that the initial part of the request has
    been received and has not yet been rejected by the server. The client
    SHOULD continue by sending the remainder of the request or, if the
    request has already been completed, ignore this response. The server
MUST send a final response after the request has been completed.
+   See section 8.2.3 for detailed discussion of the use and handling of this
+   status code.
 
 10.1.2 101 Switching Protocols
 
    The server understands and is willing to comply with the client's
-   request, via the Upgrade message header field (section 14.41), for a
+   request, via the Upgrade message header field (section 14.42), for a
    change in the application protocol being used on this connection. The
    server will switch protocols to those defined by the response's
    Upgrade header field immediately after the empty line which
    terminates the 101 response.
 
-   The protocol should only be switched when it is advantageous to do
+   The protocol SHOULD be switched only when it is advantageous to do
so. For example, switching to a newer version of HTTP is advantageous
over older versions, and switching to a real-time, synchronous protocol
-   may
+   might
be advantageous when delivering resources that use such features.
 
 10.2 Successful 2xx
 
@@ -2525,33 +2747,41 @@
    The request has succeeded. The information returned with the response
    is dependent on the method used in the request, for example:
 
GET    an entity corresponding to the requested resource is sent in the response;
 
HEAD   the entity-header fields corresponding to the requested
resource are sent in the response without any message-body;
 
POST   an entity describing or containing the result of the action;
 
TRACE  an entity containing the request message as received by the end server.
 
 10.2.2 201 Created
 
    The request has been fulfilled and resulted in a new resource being
    created. The newly created resource can be referenced by the URI(s) returned in the entity of the response, with the most specific
-   URL
+   URI
for the resource given by a Location header field.
+   The response SHOULD include an entity containing a list of resource
+   characteristics and location(s) from which the user or user agent can
+   choose the one most appropriate. The entity format is specified by
+   the media type given in the Content-Type header field.
The origin server MUST create the resource before returning the 201 status code.
If the action cannot be carried out immediately, the server 
-   should
+   SHOULD
respond with 202 (Accepted) response instead.
+
+   A 201 response MAY contain an ETag response header field indicating
+   the current value of the entity tag for the requested variant just
+   created, see section 14.19.
 
 10.2.3 202 Accepted
 
    The request has been accepted for processing, but the processing has not been completed. The request
-   MAY or MAY NOT
+   might or might not
-   eventually be acted upon, as it MAY
+   eventually be acted upon, as it might
 be disallowed when processing actually takes place. There is no facility for re-sending a status code from an
    asynchronous operation such as this.
 
    The 202 response is intentionally non-committal. Its purpose is to
@@ -2569,22 +2799,25 @@
    definitive set as available from the origin server, but is gathered
    from a local or a third-party copy. The set presented MAY be a subset
    or superset of the original version. For example, including local annotation information about the resource
-   MAY
+   might
result in a superset of the metainformation known by the origin server. Use of this
response code is not required and is only appropriate when the response would
otherwise be 200 (OK).
 
 10.2.5 204 No Content
 
The server has fulfilled the request but
-   there is no new information to send back.
+   does not need to return an entity-body, and might want to return updated metainformation.
-   If the client is a user agent, it SHOULD NOT change its document view from that which caused the request to be sent. This
-   response is primarily intended to allow input for actions to take
-   place without causing a change to the user agent's active document view.
The response MAY include new
+   or updated
metainformation in the form of entity-headers, which
-   SHOULD apply to the document currently in the user agent's active view.
+   if present SHOULD be associated with the requested variant.

+   If the client is a user agent, it SHOULD NOT change its document view
+   from that which caused the request to be sent. This response is
+   primarily intended to allow input for actions to take place without
+   causing a change to the user agent's active document view, although
+   any new or updated metainformation SHOULD be applied to the document
+   currently in the user agent's active view.
 
    The 204 response MUST NOT include a message-body, and thus is always
    terminated by the first empty line after the header fields.
@@ -2601,13 +2834,40 @@
 10.2.7 206 Partial Content
 
    The server has fulfilled the partial GET request for the resource.
-   The request must have included a Range header field (section 14.36)
+   The request MUST have included a Range header field (section 14.35)
-   indicating the desired range.
+   indicating the desired range, and MAY have included an If-Range
+   header field (section 14.27) to make the request conditional.
+
+   The response MUST include the following header fields:
+
-   The response MUST include either
+      - Either
- a Content-Range header field (section 14.17) indicating
+a Content-Range header field (section 14.16) indicating
the range included with this response, or a multipart/byteranges
-   Content-Type including Content-Range fields for each part. If
+        Content-Type including Content-Range fields for each part. If
-   multipart/byteranges is not used, the Content-Length header field in the response
+        a Content-Length header field is present in the response, its value
MUST match the actual number of OCTETs transmitted in the message-body.
+
+      - Date
+
+      - ETag and/or Content-Location, if the header would have been sent
+        in a 200 response to the same request
+
+      - Expires, Cache-Control, and/or Vary, if the field-value might
+        differ from that sent in any previous response for the same
+        variant
+
+   If the 206 response is the result of an If-Range request that used a
+   strong cache validator (see section 13.3.3), the response SHOULD NOT
+   include other entity-headers. If the response is the result of an
+   If-Range request that used a weak validator, the response MUST NOT
+   include other entity-headers; this prevents inconsistencies between
+   cached entity-bodies and updated headers. Otherwise, the response
+   MUST include all of the entity-headers that would have been returned
+   with a 200 (OK) response to the same request.
+
+   A cache MUST NOT combine a 206 response with other previously cached
+   content if the ETag or Last-Modified headers do not match exactly,
+   see 13.5.4.
 
    A cache that does not support the Range and Content-Range headers
    MUST NOT cache 206 (Partial) responses.
@@ -2615,13 +2875,16 @@
 10.3 Redirection 3xx
 
    This class of status code indicates that further action needs to be
taken by the user agent in order to fulfill the request.  The action
    required MAY be carried out by the user agent without interaction
    with the user if and only if the method used in the second request is GET or HEAD.
-   A user agent SHOULD NOT automatically redirect a request
-   more than 5 times, since such redirections usually indicate an
-   infinite loop.
+    A client SHOULD detect infinite redirection loops, since
+   such loops generate network traffic for each redirection.
 
+      Note: previous versions of this specification recommended a
+      maximum of five redirections. Content developers should be aware
+      that there might be clients that implement such a fixed
+      limitation.
 
 10.3.1 300 Multiple Choices
 
@@ -2636,59 +2899,64 @@
    which the user or user agent can choose the one most appropriate. The
    entity format is specified by the media type given in the Content-Type
     header field. Depending upon the format and the capabilities of the user agent, selection of the most appropriate choice
-   may
+   MAY
be performed automatically. However, this specification does not define
    any standard for such automatic selection.
 
    If the server has a preferred choice of representation, it SHOULD include the specific
-   URL
+  URI
    for that representation in the Location field; user agents MAY use the Location field value for automatic redirection. This response is
-   cachable unless indicated otherwise.
+   cacheable unless indicated otherwise.
 
 10.3.2 301 Moved Permanently
 
    The requested resource has been assigned a new permanent URI and any
-   future references to this resource SHOULD be done using one of the
+   future references to this resource SHOULD use one of the
returned URIs.  Clients with link editing capabilities
-   SHOULD automatically
+ ought to automatically
re-link references to the Request-URI to one or more of the new
references returned by the server, where possible. This response is
-   cachable
+   cacheable
unless indicated otherwise.
-
-   If the new URI is a location, its URL
+   The new permanent URI
SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity
of the response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s).
 
    If the 301 status code is received in response to a request
    [DEL[[INS[{2068,2616}]] other than GET or HEAD]] [INS[[INS[{errata}]] method that is known to be "safe", as defined in section 9.1.1, then the request MAY be automatically redirected by the user agent without confirmation.  Otherwise]], the user agent MUST NOT automatically redirect the
    request unless it can be confirmed by the user, since this might
    change the conditions under which the request was issued.
 
Note: When automatically redirecting a POST request after
receiving a 301 status code, some existing HTTP/1.0 user agents
will erroneously change it into a GET request.
 
-10.3.3 302 Moved Temporarily
+10.3.3 302 Found
 
    The requested resource resides temporarily under a different URI.
-   Since the redirection may be altered on occasion, the client SHOULD
+   Since the redirection might be altered on occasion, the client SHOULD
continue to use the Request-URI for future requests.  This response is only
-   cachable
+   cacheable
    if indicated by a Cache-Control or Expires header field.
 
-   If the new URI is a location, its URL
+   The temporary URI
SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity
of the response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s).
 
    If the 302 status code is received in response to a request [DEL[[INS[{2068,2616}]] other than GET or HEAD]] [INS[[INS[{errata}]] method that is known to be "safe", as defined in section 9.1.1, then the request MAY be automatically redirected by the user agent without confirmation.  Otherwise]], the user agent MUST NOT automatically redirect the
    request unless it can be confirmed by the user, since this might
    change the conditions under which the request was issued.

-     Note: When automatically redirecting a POST request after receiving
-     a 302 status code, some existing HTTP/1.0 user agents will
-     erroneously change it into a GET request.
+      Note: RFC 1945 and RFC 2068 specify that the client is not allowed
+      to change the method on the redirected request.  However, most
+      existing user agent implementations treat 302 as if it were a 303
+      response, performing a GET on the Location field-value regardless
+      of the original request method. The status codes 303 and 307 have
+      been added for servers that wish to make unambiguously clear which
+      kind of reaction is expected of the client.
 
 10.3.4 303 See Other
 
@@ -2697,31 +2965,42 @@
    exists primarily to allow the output of a POST-activated script to
    redirect the user agent to a selected resource. The new URI is not a
    substitute reference for the originally requested resource. The 303
-   response is not cachable,
+   response MUST NOT be cached,
-   but the response to the second (redirected) request MAY be cachable.
+   but the response to the second (redirected) request might be cacheable.
 
-   If the new URI is a location, its URL
+   The different URI
SHOULD be given by the Location field in the response. Unless the request method was HEAD, the entity of the
response SHOULD contain a short hypertext note with a hyperlink to
the new URI(s).
+
+      Note: Many pre-HTTP/1.1 user agents do not understand the 303
+      status. When interoperability with such clients is a concern, the
+      302 status code may be used instead, since most user agents react
+      to a 302 response as described here for 303.
 
 10.3.5 304 Not Modified
 
    If the client has performed a conditional GET request and access is
    allowed, but the document has not been modified, the server SHOULD respond with this status code. The
+  304
response MUST NOT contain a message-body
-  .
+   , and thus is always terminated by the first empty line
+   after the header fields.
 
    The response MUST include the following header fields:
 
-  o  Date
+      - Date, unless its omission is required by section 14.18.1
 
+   If a clockless origin server obeys these rules, and proxies and
+   clients add their own Date to any response received without one (as
+   already specified by [RFC 2068], section 14.19), caches will operate
+   correctly.

-  o
+      - 
ETag and/or Content-Location, if the header would have been sent
in a 200 response to the same request
-
-  o 
+      -
Expires, Cache-Control, and/or Vary, if the field-value might
differ from that sent in any previous response for the same  variant
+
+
 
    If the conditional GET used a strong cache validator (see section
    13.3.3), the response SHOULD NOT include other entity-headers.
@@ -2737,14 +3016,42 @@
    cache MUST update the entry to reflect any new field values given in
    the response.
 
-   The 304 response MUST NOT include a message-body, and thus is always
-   terminated by the first empty line after the header fields.
-
 10.3.6 305 Use Proxy
 
    The requested resource MUST be accessed through the proxy given by
-   the Location field. The Location field gives the URL of the proxy.
+   the Location field. The Location field gives the URI of the proxy.
-   The recipient is expected to repeat the request via the proxy.
+   The recipient is expected to repeat this single request via the proxy.
+   305 responses MUST only be generated by origin servers.
+
+      Note: RFC 2068 was not clear that 305 was intended to redirect a
+      single request, and to be generated by origin servers only.  Not
+      observing these limitations has significant security consequences.
+
+10.3.7 306 (Unused)
+
+   The 306 status code was used in a previous version of the
+   specification, is no longer used, and the code is reserved.
+
+10.3.8 307 Temporary Redirect
+
+   The requested resource resides temporarily under a different URI.
+   Since the redirection MAY be altered on occasion, the client SHOULD
+   continue to use the Request-URI for future requests.  This response
+   is only cacheable if indicated by a Cache-Control or Expires header
+   field.
+
+   The temporary URI SHOULD be given by the Location field in the
+   response. Unless the request method was HEAD, the entity of the
+   response SHOULD contain a short hypertext note with a hyperlink to
+   the new URI(s) , since many pre-HTTP/1.1 user agents do not
+   understand the 307 status. Therefore, the note SHOULD contain the
+   information necessary for a user to repeat the original request on
+   the new URI.
+
+   If the 307 status code is received in response to a request [DEL[other
+   than GET or HEAD]]
[INS[[INS[{errata}]] method
   that is known to be "safe", as defined in section 9.1.1, then the
   request MAY be automatically redirected by the user agent without
   confirmation.  Otherwise]], the user agent MUST NOT automatically redirect the
+   request unless it can be confirmed by the user, since this might
+   change the conditions under which the request was issued.
 
 10.4 Client Error 4xx
 
@@ -2755,15 +3062,13 @@
    condition. These status codes are applicable to any request method.
    User agents SHOULD display any included entity to the user.
 
-     Note:
If the client is sending data, a server implementation using TCP
-     should
+   SHOULD
be careful to ensure that the client acknowledges
receipt of the packet(s) containing the response, before the server closes the
input connection. If the client continues sending data
to the server after the close, the server's TCP stack will send a reset
packet to the client, which may erase the client's unacknowledged input buffers
before they can be read and interpreted by the HTTP application.
 
 10.4.1 400 Bad Request
 
@@ -2774,7 +3079,7 @@
 10.4.2 401 Unauthorized
 
    The request requires user authentication. The response MUST include a
-   WWW-Authenticate header field (section 14.46) containing a challenge
+   WWW-Authenticate header field (section 14.47) containing a challenge
    applicable to the requested resource. The client MAY repeat the
    request with a suitable Authorization header field (section 14.8). If
    the request already included Authorization credentials, then the 401
@@ -2782,9 +3087,10 @@
    credentials. If the 401 response contains the same challenge as the
    prior response, and the user agent has already attempted
    authentication at least once, then the user SHOULD be presented the
-   entity that was given in the response, since that entity MAY
+   entity that was given in the response, since that entity might
include relevant diagnostic information. HTTP access authentication is explained in
-   section 11.
+   "HTTP Authentication: Basic and Digest Access
+   Authentication" [43].
 
 10.4.3 402 Payment Required
 
@@ -2796,22 +3102,20 @@
    Authorization will not help and the request SHOULD NOT be repeated.
    If the request method was not HEAD and the server wishes to make
    public why the request has not been fulfilled, it SHOULD describe the
reason for the refusal in the entity. 
-   This status code is commonly used when the server does not wish to reveal exactly why the request
-   has been refused, or when no other response is applicable.
+   If the server does not wish to make this information available to the client, the status code 404
+   (Not Found) can be used instead.
 
 10.4.5 404 Not Found
 
    The server has not found anything matching the Request-URI. No
    indication is given of whether the condition is temporary or
permanent.
-
-   If the server does not wish to make this information available to the
-   client, the status code 403 (Forbidden) can be used instead.
The 410 (Gone) status code SHOULD be used if the server knows, through some
internally configurable mechanism, that an old resource is
permanently unavailable and has no forwarding address.
+   This status code is commonly used when the server does not wish to
+   reveal exactly why the request has been refused, or when no other
+   response is applicable.
 
 10.4.6 405 Method Not Allowed
 
@@ -2829,29 +3133,32 @@
    Unless it was a HEAD request, the response SHOULD include an entity
    containing a list of available entity characteristics and location(s)
    from which the user or user agent can choose the one most
appropriate. The entity format is specified by the media type given
    in the Content-Type header field. Depending upon the format and the
    capabilities of the user agent, selection of the most appropriate
-   choice may be performed automatically. However, this specification
+   choice MAY be performed automatically. However, this specification
    does not define any standard for such automatic selection.
 
Note: HTTP/1.1 servers are allowed to return responses which are
not acceptable according to the accept headers sent in the request.
In some cases, this may even be preferable to sending a 406 response.
User agents are encouraged to inspect the headers of
an incoming response to determine if it is acceptable.
If the response could be unacceptable, a user agent SHOULD temporarily
stop receipt of more data and query the user for a
decision on further actions.
 
 10.4.8 407 Proxy Authentication Required
 
    This code is similar to 401 (Unauthorized), but indicates that the
-   client MUST first authenticate itself with the proxy. The proxy MUST
+   client must first authenticate itself with the proxy. The proxy MUST
    return a Proxy-Authenticate header field (section 14.33) containing a
    challenge applicable to the proxy for the requested resource. The
    client MAY repeat the request with a suitable Proxy-Authorization
    header field (section 14.34). HTTP access authentication is explained in
-   section 11.
+   "HTTP Authentication: Basic and Digest Access Authentication" [43].
 
 10.4.9 408 Request Timeout
 
@@ -2865,28 +3172,30 @@
    state of the resource. This code is only allowed in situations where
    it is expected that the user might be able to resolve the conflict
    and resubmit the request. The response body SHOULD include enough
    information for the user to recognize the source of the conflict.
    Ideally, the response entity would include enough information for the user or user agent to fix the problem; however, that
-   may
+   might
    not be possible and is not required.
 
-   Conflicts are most likely to occur in response to a PUT request.
+   Conflicts are most likely to occur in response to a PUT request.
-   If versioning is
+   For example, if versioning were
being used and the entity being PUT
included changes to a resource which conflict with those made by an earlier (third-party) request, the server
-   MAY
+   might
use the 409 response to indicate that it can't complete the request. In this case, the response entity
-   SHOULD
+   would likely
contain a list of the differences between the two versions in a format defined by the response Content-Type.
 
 10.4.11 410 Gone
 
    The requested resource is no longer available at the server and no forwarding address is known. This condition
-   SHOULD
+   is expected to
be considered permanent. Clients with link editing capabilities SHOULD delete
references to the Request-URI after user approval. If the server does
not know, or has no facility to determine, whether or not the
condition is permanent, the status code 404 (Not Found) SHOULD be used instead.  This response is
-   cachable unless indicated otherwise.
+   cacheable unless indicated otherwise.
 
    The 410 response is primarily intended to assist the task of web
    maintenance by notifying the recipient that the resource is
@@ -2917,12 +3226,12 @@
 
    The server is refusing to process a request because the request
    entity is larger than the server is willing or able to process. The
-   server may close the connection to prevent the client from continuing
+   server MAY close the connection to prevent the client from continuing
    the request.
 
    If the condition is temporary, the server SHOULD include a Retry-
    After header field to indicate that it is temporary and after what
-   time the client may try again.
+   time the client MAY try again.
 
 10.4.15 414 Request-URI Too Long
 
@@ -2930,8 +3239,8 @@
    is longer than the server is willing to interpret. This rare
    condition is only likely to occur when a client has improperly
    converted a POST request to a GET request with long query
-   information, when the client has descended into a URL "black hole" of
+   information, when the client has descended into a URI "black hole" of
-   redirection (e.g., a redirected URL prefix that points to a suffix of
+   redirection (e.g., a redirected URI prefix that points to a suffix of
    itself), or when the server is under attack by a client attempting to
    exploit security holes present in some servers using fixed-length
    buffers for reading or manipulating the Request-URI.
@@ -2942,6 +3251,28 @@
    the request is in a format not supported by the requested resource
    for the requested method.
 
+10.4.17 416 Requested Range Not Satisfiable
+
+   A server SHOULD return a response with this status code if a request
+   included a Range request-header field (section 14.35), and none of
+   the range-specifier values in this field overlap the current extent
+   of the selected resource, and the request did not include an If-Range
+   request-header field. (For byte-ranges, this means that the first-
+   byte-pos of all of the byte-range-spec values were greater than the
+   current length of the selected resource.)
+
+   When this status code is returned for a byte-range request, the
+   response SHOULD include a Content-Range entity-header field
+   specifying the current length of the selected resource (see section
+   14.16). This response MUST NOT use the multipart/byteranges content-
+   type.
+
+10.4.18 417 Expectation Failed
+
+   The expectation given in an Expect request-header field (see section
+   14.20) could not be met by this server, or, if the server is a proxy,
+   the server has unambiguous evidence that the request could not be met
+   by the next-hop server.
 
 10.5 Server Error 5xx
 
@@ -2976,19 +3307,23 @@
    The server is currently unable to handle the request due to a
    temporary overloading or maintenance of the server. The implication
    is that this is a temporary condition which will be alleviated after
-   some delay. If known, the length of the delay may be indicated in a
+   some delay. If known, the length of the delay MAY be indicated in a
Retry-After header. If no Retry-After is given, the client SHOULD
    handle the response as it would for a 500 response.
 
Note: The existence of the 503 status code does not imply that a
server must use it when becoming overloaded. Some servers may wish
to simply refuse the connection.
 
 10.5.5 504 Gateway Timeout
 
    The server, while acting as a gateway or proxy, did not receive a
-   timely response from the upstream server
+   timely response from the upstream server
- it accessed
+   specified by the URI (e.g. HTTP, FTP, LDAP) or some other auxiliary server (e.g. DNS) it needed to access
in attempting to complete the request.
+
+      Note: Note to implementors: some deployed proxies are known to
+      return 400 or 500 when DNS lookups time out.
 
 10.5.6 505 HTTP Version Not Supported
 
@@ -3002,143 +3337,31 @@
 
 11 Access Authentication
 
-   HTTP provides a simple challenge-response authentication
+   HTTP provides several OPTIONAL challenge-response authentication
-   mechanism which MAY be used by a server to challenge a client request and
+   mechanisms which can be used by a server to challenge a client request and
-   by a client to provide authentication information. It uses an extensible,
+   by a client to provide authentication information.
-   case-insensitive token to identify the authentication scheme,
-   followed by a comma-separated list of attribute-value pairs which
-   carry the parameters necessary for achieving authentication via that
-   scheme.
+   The general framework for access authentication, and the specification of
+   "basic" and "digest" authentication, are specified in "HTTP
+   Authentication: Basic and Digest Access Authentication" [43]. This
+   specification adopts the definitions of "challenge" and "credentials"
+   from that specification.
-
-          auth-scheme    = token
-
-          auth-param     = token "=" quoted-string
-
-   The 401 (Unauthorized) response message is used by an origin server
-   to challenge the authorization of a user agent. This response MUST
-   include a WWW-Authenticate header field containing at least one
-   challenge applicable to the requested resource.
-
-          challenge      = auth-scheme 1*SP realm *( "," auth-param )
-
-          realm          = "realm" "=" realm-value
-          realm-value    = quoted-string
-
-   The realm attribute (case-insensitive) is required for all
-   authentication schemes which issue a challenge. The realm value
-   (case-sensitive), in combination with the canonical root URL (see
-   section 5.1.2) of the server being accessed, defines the protection
-   space. These realms allow the protected resources on a server to be
-   partitioned into a set of protection spaces, each with its own
-   authentication scheme and/or authorization database. The realm value
-   is a string, generally assigned by the origin server, which may have
-   additional semantics specific to the authentication scheme.
-
-   A user agent that wishes to authenticate itself with a server--
-   usually, but not necessarily, after receiving a 401 or 411 response-
-   -MAY do so by including an Authorization header field with the
-   request. The Authorization field value consists of credentials
-
-   containing the authentication information of the user agent for the
-   realm of the resource being requested.
-
-          credentials    = basic-credentials
-                         | auth-scheme #auth-param
-
-   The domain over which credentials can be automatically applied by a
-   user agent is determined by the protection space. If a prior request
-   has been authorized, the same credentials MAY be reused for all other
-   requests within that protection space for a period of time determined
-   by the authentication scheme, parameters, and/or user preference.
-   Unless otherwise defined by the authentication scheme, a single
-   protection space cannot extend outside the scope of its server.
-
-   If the server does not wish to accept the credentials sent with a
-   request, it SHOULD return a 401 (Unauthorized) response. The response
-   MUST include a WWW-Authenticate header field containing the (possibly
-   new) challenge applicable to the requested resource and an entity
-   explaining the refusal.
-
-   The HTTP protocol does not restrict applications to this simple
-   challenge-response mechanism for access authentication. Additional
-   mechanisms MAY be used, such as encryption at the transport level or
-   via message encapsulation, and with additional header fields
-   specifying authentication information. However, these additional
-   mechanisms are not defined by this specification.
-
-   Proxies MUST be completely transparent regarding user agent
-   authentication. That is, they MUST forward the WWW-Authenticate and
-   Authorization headers untouched, and follow the rules found in
-   section 14.8.
-
-   HTTP/1.1 allows a client to pass authentication information to and
-   from a proxy via the Proxy-Authenticate and Proxy-Authorization
-   headers.
-
-11.1 Basic Authentication Scheme
-
-   The "basic" authentication scheme is based on the model that the user
-   agent must authenticate itself with a user-ID and a password for each
-   realm. The realm value should be considered an opaque string which
-   can only be compared for equality with other realms on that server.
-   The server will service the request only if it can validate the
-   user-ID and password for the protection space of the Request-URI.
-   There are no optional authentication parameters.
-
-   Upon receipt of an unauthorized request for a URI within the
-   protection space, the server MAY respond with a challenge like the
-   following:
-
-          WWW-Authenticate: Basic realm="WallyWorld"
-
-   where "WallyWorld" is the string assigned by the server to identify
-   the protection space of the Request-URI.
-
-   To receive authorization, the client sends the userid and password,
-   separated by a single colon (":") character, within a base64  encoded
-   string in the credentials.
-
-          basic-credentials = "Basic" SP basic-cookie
-
-          basic-cookie   = <base64 [7] encoding of user-pass,
-                           except not limited to 76 char/line>
-
-          user-pass   = userid ":" password
-
-          userid      = *<TEXT excluding ":">
-
-          password    = *TEXT
-
-   Userids might be case sensitive.
-
-   If the user agent wishes to send the userid "Aladdin" and password
-   "open sesame", it would use the following header field:
-
-          Authorization: Basic QWxhZGRpbjpvcGVuIHNlc2FtZQ==
-
-   See section 15 for security considerations associated with Basic
-   authentication.
-
-11.2 Digest Authentication Scheme
-
-   A digest authentication for HTTP is specified in RFC 2069 [32].
 
 12 Content Negotiation
 
    Most HTTP responses include an entity which contains information for
    interpretation by a human user. Naturally, it is desirable to supply
    the user with the "best available" entity corresponding to the
request. Unfortunately for servers and caches, not all users have
the same preferences for what is "best," and not all user agents are
    equally capable of rendering all entity types. For that reason, HTTP
    has provisions for several mechanisms for "content negotiation" --
    the process of selecting the best representation for a given response
    when there are multiple representations available.
 
Note: This is not called "format negotiation" because the alternate
representations may be of the same media type, but use different
capabilities of that type, be in different languages, etc.
 
    Any response containing an entity-body MAY be subject to negotiation,
    including error responses.
@@ -3155,7 +3378,7 @@
 
    If the selection of the best representation for a response is made by
    an algorithm located at the server, it is called server-driven
negotiation. Selection is based on the available representations of
    the response (the dimensions over which it can vary; e.g. language,
    content-coding, etc.) and the contents of particular header fields in
    the request message or on other information pertaining to the request
@@ -3173,45 +3396,38 @@
 
    Server-driven negotiation has disadvantages:
 
1. It is impossible for the server to accurately determine what might be
"best" for any given user, since that would require complete
knowledge of both the capabilities of the user agent
and the intended use for the response (e.g., does the user want
to view it on screen or print it on paper?).
-
2. Having the user agent describe its capabilities in every
request can be both very inefficient (given that only a small
percentage of responses have multiple representations) and a
potential violation of the user's privacy.
 
3. It complicates the implementation of an origin server and the
algorithms for generating responses to a request.
 
4. It may limit a public cache's ability to use the same response
for multiple user's requests.
 
    HTTP/1.1 includes the following request-header fields for enabling
    server-driven negotiation through description of user agent
    capabilities and user preferences: Accept (section 14.1), Accept-
    Charset (section 14.2), Accept-Encoding (section 14.3), Accept-
-   Language (section 14.4), and User-Agent (section 14.42). However, an
+   Language (section 14.4), and User-Agent (section 14.43). However, an
    origin server is not limited to these dimensions and MAY vary the
    response based on any aspect of the request, including information
    outside the request-header fields or within extension header fields
    not defined by this specification.
 
-   HTTP/1.1 origin servers MUST include an appropriate Vary header field
-   (section 14.43) in any cachable response based on server-driven negotiation.
-   The Vary header field describes the dimensions over
-   which the response might vary (i.e. the dimensions over which the
-   origin server picks its "best guess" response from multiple
-   representations).
-
-   HTTP/1.1 public caches MUST recognize the Vary header field when it
-   is included in a response and obey the requirements described in
-   section 13.6 that describes the interactions between caching and
-   content negotiation.
+   The Vary  header field can be used to express the parameters the
+   server uses to select a representation that is subject to server-driven negotiation.
+    See section 13.6 for use of the Vary header field
+   by caches and section 14.44 for use of the Vary header field by
+   servers.
 
 12.2 Agent-driven Negotiation
 
@@ -3219,12 +3435,11 @@
    for a response is performed by the user agent after receiving an
    initial response from the origin server. Selection is based on a list
    of the available representations of the response included within the header fields
-   (this specification reserves the field-name Alternates, as described in appendix 19.6.2.1)
or entity-body of the initial response, with each representation identified by its own URI.
Selection from among the representations may be performed automatically
(if the user agent is capable of doing so) or manually by the user selecting from a
generated (possibly hypertext) menu.
 
    Agent-driven negotiation is advantageous when the response would vary
    over commonly-used dimensions (such as type, language, or encoding),
@@ -3263,13 +3478,7 @@
 
    This specification does not define any mechanism for transparent
    negotiation, though it also does not prevent any such mechanism from
-   being developed as an extension and used within HTTP/1.1.
+   being developed as an extension that could be used within HTTP/1.1.
-   An HTTP/1.1 cache performing transparent negotiation MUST include a Vary header
-   field in the response (defining the dimensions of its variance) if it
-   is cachable to ensure correct interoperation with all HTTP/1.1
-   clients. The agent-driven negotiation information supplied by the
-   origin server SHOULD be included with the transparently negotiated
-   response.
 
 13 Caching in HTTP
 
@@ -3280,7 +3489,6 @@
    inextricable from other aspects of the protocol, and because they
    interact with each other, it is useful to describe the basic caching
    design of HTTP separately from the detailed descriptions of methods,
    headers, response codes, etc.
 
    Caching would be useless if it did not significantly improve
@@ -3295,43 +3503,40 @@
    Requirements for performance, availability, and disconnected
    operation require us to be able to relax the goal of semantic
    transparency. The HTTP/1.1 protocol allows origin servers, caches,
    and clients to explicitly reduce transparency when necessary.
    However, because non-transparent operation may confuse non-expert
-   users, and may be incompatible with certain server applications
+   users, and might be incompatible with certain server applications
(such as those for ordering merchandise), the protocol requires that
    transparency be relaxed
 
-  o only by an explicit protocol-level request when relaxed
+  - only by an explicit protocol-level request when relaxed
by client or origin server
-
-  o  only with an explicit warning to the end user when relaxed
+   - only with an explicit warning to the end user when relaxed
by cache cache or client
 
 
    Therefore, the HTTP/1.1 protocol provides these important elements:
 
1. Protocol features that provide full semantic transparency when this
is required by all parties.
 
2. Protocol features that allow an origin server or user agent to
explicitly request and control non-transparent operation.
 
3. Protocol features that allow a cache to attach warnings to
responses that do not preserve the requested approximation of
semantic transparency.
 
    A basic principle is that it must be possible for the clients to
    detect any potential relaxation of semantic transparency.
 
-     Note: The server, cache, or client implementer may be faced with
+     Note: The server, cache, or client implementor might be faced with
design decisions not explicitly discussed in this specification. If
-     a decision may affect semantic transparency, the implementer
+     a decision might affect semantic transparency, the implementor
ought to err on the side of maintaining transparency unless a careful and
complete analysis shows significant benefits in breaking transparency.
 
 13.1.1 Cache Correctness
 
@@ -3340,26 +3545,30 @@
    sections 13.2.5, 13.2.6, and 13.12) which meets one of the following
    conditions:
 
1. It has been checked for equivalence with what the origin server
would have returned by revalidating the response with the origin
server (section 13.3);
-
2. It is "fresh enough" (see section 13.2). In the default case, this
means it meets the least restrictive freshness requirement of the
-     client, server, and cache (see section 14.9); if
+     client, origin server, and cache (see section 14.9); if
the origin server so specifies, it is the freshness requirement of the
origin server alone.
+
+         If a stored response is not "fresh enough" by the most
+         restrictive freshness requirement of both the client and the
+         origin server, in carefully considered circumstances the cache
+         MAY still return the response with the appropriate Warning
+         header (see section 13.1.5 and 14.46), unless such a response
+         is prohibited (e.g., by a "no-store" cache-directive, or by a
+         "no-cache" cache-request-directive; see section 14.9).
 
-  3. It includes a warning if the freshness demand of the client
-     or the origin server is violated (see section 13.1.5 and 14.45).
-
-  4. It is an appropriate 304 (Not Modified), 305 (Proxy Redirect),
+  3. It is an appropriate 304 (Not Modified), 305 (Proxy Redirect),
or error (4xx or 5xx) response message.
 
    If the cache can not communicate with the origin server, then a
    correct cache SHOULD respond as above if the response can be
    correctly served from the cache; if not it MUST return an error or
    warning indicating that there was a communication failure.
 
    If a cache receives a response (either an entire response, or a 304
@@ -3369,104 +3578,118 @@
    Warning (but without removing any existing Warning headers). A cache
    SHOULD NOT attempt to revalidate a response simply because that
    response became stale in transit; this might lead to an infinite
-   loop. An user agent that receives a stale response without a Warning
+   loop. A user agent that receives a stale response without a Warning
    MAY display a warning indication to the user.
 
 13.1.2 Warnings
 
    Whenever a cache returns a response that is neither first-hand nor
    "fresh enough" (in the sense of condition 2 in section 13.1.1), it
-   must attach a warning to that effect, using a Warning response-header.
+   MUST attach a warning to that effect, using a Warning general-header.
-    This warning allows clients to take appropriate action.
+   The Warning header and the currently defined warnings are described
+   in section 14.46. The warning allows clients to take appropriate
+   action.
 
-   Warnings may be used for other purposes, both cache-related and
+   Warnings MAY be used for other purposes, both cache-related and
    otherwise. The use of a warning, rather than an error status code,
    distinguish these responses from true failures.
 
-   Warnings are always cachable, because they never weaken the
-   transparency of a response. This means that warnings can be passed to
-   HTTP/1.0 caches without danger; such caches will simply pass the
-   warning along as an entity-header in the response.
-
-   Warnings are assigned numbers between 0 and 99. This specification
+   Warnings are assigned three digit warn-codes.
-   defines the code numbers and meanings of each currently assigned
-   warnings, allowing a client or cache to take automated action in some
-   (but not all) cases.
+   The first digit indicates whether the Warning MUST or MUST NOT be deleted from a
+   stored cache entry after a successful revalidation:
+
+   1xx  Warnings that describe the freshness or revalidation status of
+     the response, and so MUST be deleted after a successful
+     revalidation. 1XX warn-codes MAY be generated by a cache only when
+     validating a cached entry. It MUST NOT be generated by clients.
+
+   2xx  Warnings that describe some aspect of the entity body or entity
+     headers that is not rectified by a revalidation (for example, a
+     lossy compression of the entity bodies) and which MUST NOT be
+     deleted after a successful revalidation.
+
+   See section 14.46 for the definitions of the codes themselves.
+
+   HTTP/1.0 caches will cache all Warnings in responses, without
+   deleting the ones in the first category. Warnings in responses that
+   are passed to HTTP/1.0 caches carry an extra warning-date field,
+   which prevents a future HTTP/1.1 recipient from believing an
+   erroneously cached Warning.
 
-   Warnings also carry a warning text. The text may be in any
+   Warnings also carry a warning text. The text MAY be in any
    appropriate natural language (perhaps based on the client's Accept
-   headers), and include an optional indication of what character set is
+   headers), and include an OPTIONAL indication of what character set is
    used.
 
-   Multiple warnings may be attached to a response (either by the origin
+   Multiple warnings MAY be attached to a response (either by the origin
    server or by a cache), including multiple warnings with the same code
-   number. For example, a server may provide the same warning with texts
-   in both English and Basque.
+   number. For example, a server might provide the same warning with
+   texts in both English and Basque.
 
-   When multiple warnings are attached to a response, it may not be
+   When multiple warnings are attached to a response, it might not be
    practical or reasonable to display all of them to the user. This
    version of HTTP does not specify strict priority rules for deciding
    which warnings to display and in what order, but does suggest some
    heuristics.
 
-   The Warning header and the currently defined warnings are described
-   in section 14.45.
-
 13.1.3 Cache-control Mechanisms
 
    The basic cache mechanisms in HTTP/1.1 (server-specified expiration
    times and validators) are implicit directives to caches. In some
-   cases, a server or client may need to provide explicit directives to
+   cases, a server or client might need to provide explicit directives to
the HTTP caches. We use the Cache-Control header for this purpose.
 
    The Cache-Control header allows a client or server to transmit a
    variety of directives in either requests or responses. These
    directives typically override the default caching algorithms. As a
    general rule, if there is any apparent conflict between header
-   values, the most restrictive interpretation should be applied (that
+   values, the most restrictive interpretation is applied (that
is, the one that is most likely to preserve semantic transparency). However,
-   in some cases, Cache-Control directives are explicitly
+   in some cases, cache-control directives are explicitly
specified as weakening the approximation of semantic transparency
(for example, "max-stale" or "public").
 
-   The Cache-Control directives are described in detail in section 14.9.
+   The cache-control directives are described in detail in section 14.9.
 
 13.1.4 Explicit User Agent Warnings
 
    Many user agents make it possible for users to override the basic
-   caching mechanisms. For example, the user agent may allow the user
+   caching mechanisms. For example, the user agent might allow the user
to specify that cached entities (even explicitly stale ones) are never
validated. Or the user agent might habitually add "Cache-Control: max-stale=3600"
-   to every request. The user should have to explicitly request
+    to every request. The user agent SHOULD NOT default to
either non-transparent behavior, or behavior that results in
abnormally ineffective caching
+   , but MAY be explicitly configured
+   to do so by an explicit action of the user
.
 
    If the user has overridden the basic caching mechanisms, the user
-   agent should explicitly indicate to the user whenever this results in
+   agent SHOULD explicitly indicate to the user whenever this results in
    the display of information that might not meet the server's
    transparency requirements (in particular, if the displayed entity is
    known to be stale). Since the protocol normally allows the user agent
    to determine if responses are stale or not, this indication need only
    be displayed when this actually happens. The indication need not be a
    dialog box; it could be an icon (for example, a picture of a rotting
-   fish) or some other visual indicator.
+   fish) or some other indicator.
 
    If the user has overridden the caching mechanisms in a way that would
-   abnormally reduce the effectiveness of caches, the user agent should
+   abnormally reduce the effectiveness of caches, the user agent SHOULD
-   continually display an indication (for example, a picture
+   continually indicate this state to the user (for example, by a display of a picture
of currency in flames) so that the user does not inadvertently consume excess
resources or suffer from excessive latency.
 
 13.1.5 Exceptions to the Rules and Warnings
 
-   In some cases, the operator of a cache may choose to configure it to
+   In some cases, the operator of a cache MAY choose to configure it to
    return stale responses even when not requested by clients. This
-   decision should not be made lightly, but may be necessary for reasons
+   decision ought not be made lightly, but may be necessary for reasons
    of availability or performance, especially when the cache is poorly
    connected to the origin server. Whenever a cache returns a stale
-   response, it MUST mark it as such (using a Warning header). This allows
+   response, it MUST mark it as such (using a Warning header) enabling
the client software to alert the user that there might be a potential problem.
 
    It also allows the user agent to take steps to obtain a first-hand or
    fresh response. For this reason, a cache SHOULD NOT return a stale
@@ -3477,24 +3700,24 @@
 
    While the origin server (and to a lesser extent, intermediate caches,
    by their contribution to the age of a response) are the primary
-   source of expiration information, in some cases the client may need
+   source of expiration information, in some cases the client might need
    to control a cache's decision about whether to return a cached
    response without validating it. Clients do this using several
    directives of the Cache-Control header.
 
-   A client's request may specify the maximum age it is willing to
+   A client's request MAY specify the maximum age it is willing to
    accept of an unvalidated response; specifying a value of zero forces
-   the cache(s) to revalidate all responses. A client may also specify
+   the cache(s) to revalidate all responses. A client MAY also specify
    the minimum time remaining before a response expires. Both of these
    options increase constraints on the behavior of caches, and so cannot
    further relax the cache's approximation of semantic transparency.
 
-   A client may also specify that it will accept stale responses, up to
+   A client MAY also specify that it will accept stale responses, up to
    some maximum amount of staleness. This loosens the constraints on the
-   caches, and so may violate the origin server's specified
+   caches, and so might violate the origin server's specified
-   constraints on semantic transparency, but may be necessary to
+   constraints on semantic transparency, but might be necessary to
support disconnected operation, or high availability in the face of poor connectivity.
 
 13.2 Expiration Model
 
@@ -3503,9 +3726,8 @@
    HTTP caching works best when caches can entirely avoid making
    requests to the origin server. The primary mechanism for avoiding
    requests is for an origin server to provide an explicit expiration
-   time in the future, indicating that a response may be used to satisfy
+   time in the future, indicating that a response MAY be used to satisfy
subsequent requests. In other words, a cache can return a fresh
response without first contacting the server.
 
    Our expectation is that servers will assign future explicit
@@ -3520,14 +3742,14 @@
    requesting client.
 
    If an origin server wishes to force a semantically transparent cache
-   to validate every request, it may assign an explicit expiration time
+   to validate every request, it MAY assign an explicit expiration time
    in the past. This means that the response is always stale, and so the
    cache SHOULD validate it before using it for subsequent requests. See
    section 14.9.4 for a more restrictive way to force revalidation.
 
    If an origin server wishes to force any HTTP/1.1 cache, no matter how
-   it is configured, to validate every request, it should use the
+   it is configured, to validate every request, it SHOULD use the 
-   "must-revalidate" Cache-Control directive (see section 14.9).
+   "must-revalidate" cache-control directive (see section 14.9).
 
    Servers specify explicit expiration times using either the Expires
    header, or the max-age directive of the Cache-Control header.
@@ -3536,7 +3758,7 @@
    its display or reload a resource; its semantics apply only to caching
    mechanisms, and such mechanisms need only check a resource's
    expiration status when a new request for that resource is initiated.
-   See section 13.13 for explanation of the difference between caches
+   See section 13.13 for an explanation of the difference between caches
    and history mechanisms.
 
 13.2.2 Heuristic Expiration
@@ -3547,7 +3769,7 @@
    time) to estimate a plausible expiration time. The HTTP/1.1
    specification does not provide specific algorithms, but does impose
    worst-case constraints on their results. Since heuristic expiration
-   times may compromise semantic transparency, they should be used
+   times might compromise semantic transparency, they ought to used
    cautiously, and we encourage origin servers to provide explicit
    expiration times as much as possible.
 
@@ -3560,21 +3782,20 @@
 
    In this discussion, we use the term "now" to mean "the current value
    of the clock at the host performing the calculation." Hosts that use
-   HTTP, but especially hosts running origin servers and caches, should
+   HTTP, but especially hosts running origin servers and caches, SHOULD
    use NTP [28] or some similar protocol to synchronize their clocks to
    a globally accurate time standard.
 
-   Also note that HTTP/1.1 requires origin servers to send a Date header
+   HTTP/1.1 requires origin servers to send a Date header, if possible,
    with every response, giving the time at which the response was
-   generated. We use the term "date_value" to denote the value of
+   generated (see section 14.18). We use the term "date_value" to denote the value of
the Date header, in a form appropriate for arithmetic operations.
 
-   HTTP/1.1 uses the Age response-header to help convey age information
+   HTTP/1.1 uses the Age response-header to convey the estimated age of
-   between caches. The Age header value is the sender's
+   the response message when obtained from a cache. The Age field value is the cache's
estimate of the amount of time since the response was generated
-   at the origin server.
+   or revalidated by the origin server.
-   In the case of a cached response that has been revalidated with the origin server, the Age value is based on the time of revalidation,
-   not of the original response.
 
    In essence, the Age value is the sum of the time that the response
    has been resident in each of the caches along the path from the
@@ -3586,45 +3807,38 @@
 
    A response's age can be calculated in two entirely independent ways:
 
1. now minus date_value, if the local clock is reasonably well
synchronized to the origin server's clock. If the result is
negative, the result is replaced by zero.
 
2. age_value, if all of the caches along the response path implement HTTP/1.1.
 
    Given that we have two independent ways to compute the age of a
    response when it is received, we can combine these as

corrected_received_age = max(now - date_value, age_value)
 
    and as long as we have either nearly synchronized clocks or all-HTTP/1.1 paths, one gets a reliable (conservative) result.
 
-   Note that this correction is applied at each HTTP/1.1 cache along the
-   path, so that if there is an HTTP/1.0 cache in the path, the correct
-   received age is computed as long as the receiving cache's clock is
-   nearly in sync. We don't need end-to-end clock synchronization
-   (although it is good to have), and there is no explicit clock
-   synchronization step.
-
-   Because of network-imposed delays, some significant interval may pass from
+   Because of network-imposed delays, some significant interval might pass between
the time that a server generates a response and the time it is
received at the next outbound cache or client. If uncorrected, this
delay could result in improperly low ages.
 
    Because the request that resulted in the returned Age value must have
    been initiated prior to that Age value's generation, we can correct
    for delays imposed by the network by recording the time at which the
    request was initiated. Then, when an Age value is received, it MUST
    be interpreted relative to the time the request was initiated, not
    the time that the response was received. This algorithm results in
    conservative behavior no matter how much delay is experienced. So, we
    compute:
 
corrected_initial_age = corrected_received_age + (now - request_time)
 
    where "request_time" is the time (according to the local clock) when
    the request that elicited this response was sent.
@@ -3647,24 +3861,28 @@
        * now
        *      is the current (local) time
        */
       apparent_age = max(0, response_time - date_value);
       corrected_received_age = max(apparent_age, age_value);
       response_delay = response_time - request_time;
       corrected_initial_age = corrected_received_age + response_delay;
       resident_time = now - response_time;
       current_age   = corrected_initial_age + resident_time;
 
-   When a cache sends a response, it must add to the
-   corrected_initial_age the amount of time that the response was
-   resident locally. It must then transmit this total age, using the Age
-   header, to the next recipient cache.
+   The current_age of a cache entry is calculated by adding the amount
+   of time (in seconds) since the cache entry was last validated by the
+   origin server to the corrected_initial_age. When a response is
+   generated from a cache entry, the cache MUST include a single Age
+   header field in the response with a value equal to the cache entry's
+   current_age.
+
-
-     Note that a client cannot reliably tell that a response is first-hand,
-      but the presence of an Age header indicates that a response
-     is definitely not first-hand. Also, if the Date in a response is
-     earlier than the client's local request time, the response is
-     probably not first-hand (in the absence of serious clock skew).
+   The presence of an Age header field in a response implies that a
+   response is not first-hand. However, the converse is not true, since
+   the lack of an Age header field in a response does not imply that the
+   response is first-hand unless all caches along the request path are
+   compliant with HTTP/1.1 (i.e., older HTTP caches did not implement
+   the Age header field).
 
 13.2.4 Expiration Calculations
 
@@ -3677,28 +3895,27 @@
 
    We use the term "expires_value" to denote the value of the Expires
    header. We use the term "max_age_value" to denote an appropriate
-   value of the number of seconds carried by the max-age directive of
+   value of the number of seconds carried by the "max-age" directive of
-   the Cache-Control header in a response (see section 14.10.
+   the Cache-Control header in a response (see section 14.9.3).
 
    The max-age directive takes priority over Expires, so if max-age is
    present in a response, the calculation is simply:

freshness_lifetime = max_age_value
 
    Otherwise, if Expires is present in the response, the calculation is:

freshness_lifetime = expires_value - date_value
 
    Note that neither of these calculations is vulnerable to clock skew,
    since all of the information comes from the origin server.
 
-   If neither Expires nor Cache-Control: max-age
+   If none of Expires, Cache-Control: max-age, or Cache-Control: s-maxage (see section 14.9.3)
appears in the response, and the response does not include other restrictions on
caching, the cache MAY compute a freshness lifetime using a heuristic.
-   If the value is greater than 24 hours, the cache must attach Warning 13 to any response whose age is more than 24 hours if
+   The cache MUST attach Warning 113 to any response whose age is more than 24 hours if
such warning has not already been added.
 
    Also, if the response does have a Last-Modified time, the heuristic
    expiration value SHOULD be no more than some fraction of the interval
@@ -3707,7 +3924,7 @@
    The calculation to determine if a response has expired is quite
    simple:

response_is_fresh = (freshness_lifetime > current_age)
 
 13.2.5 Disambiguating Expiration Values
 
@@ -3724,15 +3941,15 @@
 
    If a cache has two fresh responses for the same representation with
    different validators, it MUST use the one with the more recent Date
-   header. This situation may arise because the cache is pooling
+   header. This situation might arise because the cache is pooling
    responses from other caches, or because a client has asked for a
    reload or a revalidation of an apparently fresh cache entry.
 
 13.2.6 Disambiguating Multiple Responses
 
-   Because a client may be receiving responses via multiple paths, so
+   Because a client might be receiving responses via multiple paths, so
    that some responses flow through one set of caches and other
-   responses flow through a different set of caches, a client may
+   responses flow through a different set of caches, a client might
    receive responses in an order different from that in which the origin
    server sent them. We would like the client to use the most recently
    generated response, even if older responses are still apparently
@@ -3740,28 +3957,26 @@
 
    Neither the entity tag nor the expiration value can impose an
    ordering on responses, since it is possible that a later response
intentionally carries an earlier expiration time.
-   However, the HTTP/1.1 specification requires the transmission of Date headers on
-   every response, and the Date values are ordered to a granularity of
-   one second.
+   The Date values are ordered to a granularity of one second.
 
    When a client tries to revalidate a cache entry, and the response it
    receives contains a Date header that appears to be older than the one
    for the existing entry, then the client SHOULD repeat the request
    unconditionally, and include

Cache-Control: max-age=0
 
    to force any intermediate caches to validate their copies directly
    with the origin server, or

Cache-Control: no-cache
 
    to force any intermediate caches to obtain a new copy from the origin
    server.
 
-   If the Date values are equal, then the client may use either response
+   If the Date values are equal, then the client MAY use either response
-   (or may, if it is being extremely prudent, request a new response).
+   (or MAY, if it is being extremely prudent, request a new response).
    Servers MUST NOT depend on clients being able to choose
    deterministically between responses generated during the same second,
    if their expiration times overlap.
@@ -3772,7 +3987,7 @@
    response to a client's request, it first has to check with the origin
    server (or possibly an intermediate cache with a fresh response) to
    see if its cached entry is still usable. We call this "validating"
-   the cache entry.  Since we do not want to have to pay the overhead of
+   the cache entry. Since we do not want to have to pay the overhead of
    retransmitting the full response if the cached entry is good, and we
    do not want to pay the overhead of an extra round trip if the cached
    entry is invalid, the HTTP/1.1 protocol supports the use of
@@ -3787,14 +4002,12 @@
    request.
 
    The server then checks that validator against the current validator
-   for the entity, and, if they match, it responds
+   for the entity, and, if they match (see section 13.3.3), it responds
with a special status code (usually, 304 (Not Modified)) and no entity-body.
Otherwise, it returns a full response (including entity-body). Thus, we avoid
transmitting the full response if the validator matches, and we avoid
an extra round trip if it does not match.
-
-     Note: the comparison functions used to decide if validators match
-     are defined in section 13.3.3.
 
    In HTTP/1.1, a conditional request looks exactly the same as a normal
    request for the same resource, except that it carries a special
@@ -3806,13 +4019,13 @@
    a method be performed if and only if a validator matches or if and
    only if no validators match.

Note: a response that lacks a validator may still be cached, and
served from cache until it expires, unless this is explicitly
-     prohibited by a Cache-Control directive. However, a cache cannot
+     prohibited by a cache-control directive. However, a cache cannot
do a conditional retrieval if it does not have a validator for the
entity, which means it will not be refreshable after it expires.
 
-13.3.1 Last-modified Dates
+13.3.1 Last-Modified Dates
 
    The Last-Modified entity-header field value is often used as a cache
    validator. In simple terms, a cache entry is considered to be valid
@@ -3820,15 +4033,15 @@
 
 13.3.2 Entity Tag Cache Validators
 
-   The ETag entity-header field value, an entity tag, provides for an
+   The ETag response-header field value, an entity tag, provides for an
-   "opaque" cache validator. This may allow more reliable validation
+   "opaque" cache validator. This might allow more reliable validation
in situations where it is inconvenient to store modification dates,
    where the one-second resolution of HTTP date values is not
    sufficient, or where the origin server wishes to avoid certain
-   paradoxes that may arise from the use of modification dates.
+   paradoxes that might arise from the use of modification dates.
 
    Entity Tags are described in section 3.11. The headers used with
-   entity tags are described in sections 14.20, 14.25, 14.26 and 14.43.
+   entity tags are described in sections 14.19, 14.24, 14.26 and 14.44.
 
 13.3.3 Weak and Strong Validators
 
@@ -3836,12 +4049,11 @@
    decide if they represent the same or different entities, one normally
    would expect that if the entity (the entity-body or any entity-
    headers) changes in any way, then the associated validator would
-   change as well.  If this is true, then we call this validator a
+   change as well. If this is true, then we call this validator a
    "strong validator."
 
-   However, there may be cases when a server prefers to change the
+   However, there might be cases when a server prefers to change the
    validator only on semantically significant changes, and not when
    insignificant aspects of the entity change. A validator that does not
    always change when the resource changes is a "weak validator."
 
@@ -3849,50 +4061,51 @@
    provides a mechanism to tag an entity tag as "weak." One can think of
    a strong validator as one that changes whenever the bits of an entity
    changes, while a weak value changes whenever the meaning of an entity
-   changes.  Alternatively, one can think of a strong validator as part
+   changes. Alternatively, one can think of a strong validator as part
    of an identifier for a specific entity, while a weak validator is
    part of an identifier for a set of semantically equivalent entities.

Note: One example of a strong validator is an integer that is
incremented in stable storage every time an entity is changed.

An entity's modification time, if represented with one-second
resolution, could be a weak validator, since it is possible that
-     the resource may be modified twice during a single second.
+     the resource might be modified twice during a single second.
-
-     Support for weak validators is optional; however, weak validators
+     Support for weak validators is optional. However, weak validators
allow for more efficient caching of equivalent objects; for
example, a hit counter on a site is probably good enough if it is
updated every few days or weeks, and any value during that period
is likely "good enough" to be equivalent.

A "use" of a validator is either when a client generates a request
and includes the validator in a validating header field, or when a
server compares two validators.
 
    Strong validators are usable in any context. Weak validators are only
    usable in contexts that do not depend on exact equality of an entity.
    For example, either kind is usable for a conditional GET of a full
    entity. However, only a strong validator is usable for a sub-range
-   retrieval, since otherwise the client may end up with an internally
+   retrieval, since otherwise the client might end up with an internally
    inconsistent entity.
 
+   Clients MAY issue simple (non-subrange) GET requests with either weak
+   validators or strong validators. Clients MUST NOT use weak validators
+   in other forms of request.
+
    The only function that the HTTP/1.1 protocol defines on validators is
    comparison. There are two validator comparison functions, depending
    on whether the comparison context allows the use of weak validators
    or not:
 
-  o  The strong comparison function: in order to be considered equal,
+   - The strong comparison function: in order to be considered equal,
-     both validators must be identical in every way, and neither may be weak.
+     both validators MUST be identical in every way, and both MUST NOT be weak.

-  o  The weak comparison function: in order to be considered equal,
+   - The weak comparison function: in order to be considered equal,
-     both validators must be identical in every way, but either or
+     both validators MUST be identical in every way, but either or
-     both of them may be tagged as "weak" without affecting the result.
+     both of them MAY be tagged as "weak" without affecting the result.
-
-   The weak comparison function MAY be used for simple (non-subrange)
-
-   GET requests. The strong comparison function MUST be used in all
-   other cases.

    An entity tag is strong unless it is explicitly tagged as weak.
    Section 3.11 gives the syntax for entity tags.
@@ -3901,28 +4114,35 @@
    implicitly weak unless it is possible to deduce that it is strong,
    using the following rules:
 
-  o  The validator is being compared by an origin server to the
+   - The validator is being compared by an origin server to the
actual current validator for the entity and,
-  o  That origin server reliably knows that the associated entity did
+   - That origin server reliably knows that the associated entity did
not change twice during the second covered by the presented validator.

or

-  o  The validator is about to be used by a client in an If-Modified-Since
+   - The validator is about to be used by a client in an If-Modified-Since
or If-Unmodified-Since header, because the client has a cache
entry for the associated entity, and
-  o  That cache entry includes a Date value, which gives the time
+   - That cache entry includes a Date value, which gives the time
when the origin server sent the original response, and
-  o  The presented Last-Modified time is at least 60 seconds before
+   - The presented Last-Modified time is at least 60 seconds before
the Date value.

or

-  o  The validator is being compared by an intermediate cache to the
+   - The validator is being compared by an intermediate cache to the
validator stored in its cache entry for the entity, and
-  o  That cache entry includes a Date value, which gives the time
+   - That cache entry includes a Date value, which gives the time
when the origin server sent the original response, and
-  o  The presented Last-Modified time is at least 60 seconds before
+   - The presented Last-Modified time is at least 60 seconds before
the Date value.
 
    This method relies on the fact that if two different responses were
    sent by the origin server during the same second, but both had the
@@ -3931,39 +4151,42 @@
    second limit guards against the possibility that the Date and Last-
    Modified values are generated from different clocks, or at somewhat
    different times during the preparation of the response. An
-   implementation may use a value larger than 60 seconds, if it is
+   implementation MAY use a value larger than 60 seconds, if it is
    believed that 60 seconds is too short.
 
    If a client wishes to perform a sub-range retrieval on a value for
    which it has only a Last-Modified time and no opaque validator, it
-   may do this only if the Last-Modified time is strong in the sense
+   MAY do this only if the Last-Modified time is strong in the sense
    described here.
 
-   A cache or origin server receiving a cache-conditional request, other than
+   A cache or origin server receiving a conditional request, other than
a full-body GET request, MUST use the strong comparison function to
evaluate the condition.
 
    These rules allow HTTP/1.1 caches and clients to safely perform sub-range
     retrievals on values that have been obtained from HTTP/1.0
    servers.
 
-13.3.4 Rules for When to Use Entity Tags and Last-modified Dates
+13.3.4 Rules for When to Use Entity Tags and Last-Modified Dates
 
    We adopt a set of rules and recommendations for origin servers,
-   clients, and caches regarding when various validator types should
+   clients, and caches regarding when various validator types ought to
be used, and for what purposes.
 
    HTTP/1.1 origin servers:
 
-  o  SHOULD send an entity tag validator unless it is not feasible to
+   - SHOULD send an entity tag validator unless it is not feasible to
generate one.
-  o  MAY send a weak entity tag instead of a strong entity tag, if
+   - MAY send a weak entity tag instead of a strong entity tag, if
performance considerations support the use of weak entity tags,
or if it is unfeasible to send a strong entity tag.
-  o  SHOULD send a Last-Modified value if it is feasible to send one,
+   - SHOULD send a Last-Modified value if it is feasible to send one,
unless the risk of a breakdown in semantic transparency that could
result from using this date in an If-Modified-Since header would
lead to serious problems.
 
    In other words, the preferred behavior for an HTTP/1.1 origin server
    is to send both a strong entity tag and a Last-Modified value.
@@ -3973,52 +4196,62 @@
    change whenever the associated entity changes in a semantically
    significant way.

Note: in order to provide semantically transparent caching, an
origin server must avoid reusing a specific strong entity tag value
for two different entities, or reusing a specific weak entity tag
-     value for two semantically different entities. Cache entries may
+     value for two semantically different entities. Cache entries might
persist for arbitrarily long periods, regardless of expiration
-     times, so it may be inappropriate to expect that a
+     times, so it might be inappropriate to expect that a
cache will never again attempt to validate an entry using a validator that it
obtained at some point in the past.
 
    HTTP/1.1 clients:
 
-     o  If an entity tag has been provided by the origin server, MUST
+      - If an entity tag has been provided by the origin server, MUST
use that entity tag in any cache-conditional request (using 
If-Match or If-None-Match).
 
-     o  If only a Last-Modified value has been provided by the origin
+      - If only a Last-Modified value has been provided by the origin
         server, SHOULD use that value in non-subrange cache-conditional
         requests (using If-Modified-Since).
-     o  If only a Last-Modified value has been provided by an HTTP/1.0
+      - If only a Last-Modified value has been provided by an HTTP/1.0
         origin server, MAY use that value in subrange cache-conditional
-        requests (using If-Unmodified-Since:). The user agent should
+        requests (using If-Unmodified-Since:). The user agent SHOULD
         provide a way to disable this, in case of difficulty.
-     o  If both an entity tag and a Last-Modified value have been
+      - If both an entity tag and a Last-Modified value have been
         provided by the origin server, SHOULD use both validators in
         cache-conditional requests. This allows both HTTP/1.0 and
         HTTP/1.1 caches to respond appropriately.
 
-   An HTTP/1.1 cache, upon receiving a request, MUST use the most
-   restrictive validator when deciding whether the client's cache entry
-   matches the cache's own cache entry. This is only an issue when the
-   request contains both an entity tag and a last-modified-date
-   validator (If-Modified-Since or If-Unmodified-Since).
+   An HTTP/1.1 origin server, upon receiving a conditional request that
+   includes both a Last-Modified date (e.g., in an If-Modified-Since or
+   If-Unmodified-Since header field) and one or more entity tags (e.g.,
+   in an If-Match, If-None-Match, or If-Range header field) as cache
+   validators, MUST NOT return a response status of 304 (Not Modified)
+   unless doing so is consistent with all of the conditional header
+   fields in the request.
+
+   An HTTP/1.1 caching proxy, upon receiving a conditional request that
+   includes both a Last-Modified date and one or more entity tags as
+   cache validators, MUST NOT return a locally cached response to the
+   client unless that cached response is consistent with all of the
+   conditional header fields in the request.
+
-     A note on rationale: The general principle behind these rules is
+      Note: The general principle behind these rules is
that HTTP/1.1 servers and clients should transmit as much non-redundant
information as is available in their responses and requests.
HTTP/1.1 systems receiving this information will make the most
conservative assumptions about the validators they receive.

HTTP/1.0 clients and caches will ignore entity tags. Generally,
last-modified values received or used by these systems will support
transparent and efficient caching, and so HTTP/1.1 origin servers
should provide Last-Modified values. In those rare cases where the
use of a Last-Modified value as a validator by an HTTP/1.0 system
could result in a serious problem, then HTTP/1.1 origin servers
should not provide one.
 
 13.3.5 Non-validating Conditionals
 
@@ -4026,60 +4259,61 @@
    knows the semantics of a resource well enough to select an
    appropriate cache validation mechanism, and the specification of any
    validator comparison function more complex than byte-equality would
-   open up a can of worms.  Thus, comparisons of any other headers
+   open up a can of worms. Thus, comparisons of any other headers
    (except Last-Modified, for compatibility with HTTP/1.0) are never
    used for purposes of validating a cache entry.
 
-13.4 Response Cachability
+13.4 Response Cacheability
-
-   Unless specifically constrained by a Cache-Control (section 14.9)
+   Unless specifically constrained by a cache-control (section 14.9)
-   directive, a caching system may always store a successful response
+   directive, a caching system MAY always store a successful response
-   (see section 13.8) as a cache entry, may return it without validation
+   (see section 13.8) as a cache entry, MAY return it without validation
-   if it is fresh, and may return it after successful validation. If
+   if it is fresh, and MAY return it after successful validation. If
    there is neither a cache validator nor an explicit expiration time
    associated with a response, we do not expect it to be cached, but
-   certain caches may violate this expectation (for example, when little
+   certain caches MAY violate this expectation (for example, when little
    or no network connectivity is available). A client can usually detect
    that such a response was taken from a cache by comparing the Date
    header to the current time.
 
-     Note that some HTTP/1.0 caches are known to violate this
+     Note: some HTTP/1.0 caches are known to violate this
expectation without providing any Warning.
 
-   However, in some cases it may be inappropriate for a cache to
+   However, in some cases it might be inappropriate for a cache to
retain an entity, or to return it in response to a subsequent request. This
-   may be because absolute semantic transparency is
+   might be because absolute semantic transparency is
deemed necessary by the service author, or because of security or privacy
-   considerations. Certain Cache-Control directives are therefore
+   considerations. Certain cache-control directives are therefore
provided so that the server can indicate that certain resource entities,
-   or portions thereof, may not be cached regardless of other considerations.
+   or portions thereof, are not to be cached regardless of other considerations.
 
    Note that section 14.8 normally prevents a shared cache from saving
    and returning a response to a previous request if that request
    included an Authorization header.
 
    A response received with a status code of 200, 203, 206, 300, 301 or
-   410 may be stored by a cache and used in reply to a subsequent
+   410 MAY be stored by a cache and used in reply to a subsequent
-   request, subject to the expiration mechanism, unless a Cache-Control
+   request, subject to the expiration mechanism, unless a cache-control
    directive prohibits caching. However, a cache that does not support
    the Range and Content-Range headers MUST NOT cache 206 (Partial
    Content) responses.
 
-   A response received with any other status code
+   A response received with any other status code (e.g. status codes 302 and 307)
MUST NOT be returned in a reply to a subsequent request unless there are
-   Cache-Control directives or another header(s) that
+   cache-control directives or another header(s) that
explicitly allow it. For example, these include the following: an Expires header (section 14.21);
-   a "max-age", "must-revalidate", "proxy-revalidate", "public" or "private" Cache-Control directive (section 14.9).
+   a "max-age", "s-maxage",  "must-revalidate", "proxy-revalidate", "public" or "private" cache-control directive (section 14.9).
 
 13.5 Constructing Responses From Caches
 
    The purpose of an HTTP cache is to store information received in
-   response to requests, for use in responding to future requests. In
+   response to requests for use in responding to future requests. In
    many cases, a cache simply returns the appropriate parts of a
    response to the requester. However, if the cache holds a cache entry
-   based on a previous response, it may have to combine parts of a new
+   based on a previous response, it might have to combine parts of a new
    response with what is held in the cache entry.
 
 13.5.1 End-to-end and Hop-by-hop Headers
@@ -4087,100 +4321,140 @@
    For the purpose of defining the behavior of caches and non-caching
    proxies, we divide HTTP headers into two categories:
 
-  o  End-to-end headers, which must be transmitted to the
+   - End-to-end headers, which are  transmitted to the
ultimate recipient of a request or response. End-to-end headers in
-     responses must be stored as part of a cache entry and
+     responses MUST be stored as part of a cache entry and MUST be
transmitted in any response formed from a cache entry.
-  o  Hop-by-hop headers, which are meaningful only for a single
+   - Hop-by-hop headers, which are meaningful only for a single
transport-level connection, and are not stored by caches or
forwarded by proxies.
 
    The following HTTP/1.1 headers are hop-by-hop headers:
 
-     o  Connection
+      - Connection
-     o  Keep-Alive
+      - Keep-Alive
-     o  Public
-     o  Proxy-Authenticate
+      - Proxy-Authenticate
+      - Proxy-Authorization
+      - TE
+      - Trailer[DEL[s [INS[{errata}]]]]
-     o  Transfer-Encoding
+      - Transfer-Encoding
-     o  Upgrade
+      - Upgrade
 
    All other headers defined by HTTP/1.1 are end-to-end headers.
 
-   Hop-by-hop headers introduced in future versions of HTTP MUST be
-   listed in a Connection header, as described in section 14.10.
+   Other hop-by-hop headers MUST be listed in a Connection header,
+   (section 14.10) to be introduced into HTTP/1.1 (or later).
 
 13.5.2 Non-modifiable Headers
 
    Some features of the HTTP/1.1 protocol, such as Digest
    Authentication, depend on the value of certain end-to-end headers. A
-   cache or non-caching
+   transparent
proxy SHOULD NOT modify an end-to-end header
unless the definition of that header requires or specifically allows that.
-  
-
-   A cache or non-caching proxy MUST NOT modify any of the following
-   fields in a request or response, nor may it add any of these fields
-   if not already present:
-
-     o  Content-Location
-     o  ETag
-     o  Expires
-     o  Last-Modified
-
-
-   A cache or non-caching proxy MUST NOT modify or add
+   A transparent proxy MUST NOT modify
any of the following fields in a
-    response that contains the no-transform Cache-Control directive, or in any request:
+   request or response, and it MUST NOT add any of these fields if not already present:
-
-     o  Content-Encoding
-     o  Content-Length
-     o  Content-Range
-     o  Content-Type
+      - Content-Location
+      - Content-MD5
+      - ETag
+      - Last-Modified
-
+   A transparent proxy MUST NOT modify any of the following fields in a
+   response:
+
+      - Expires
+
+   but it MAY add any of these fields if not already present. If an
+   Expires header is added, it MUST be given a field-value identical to
+   that of the Date header in that response.
+
+   A  proxy MUST NOT modify or add any of the following fields in a
+   message that contains the no-transform cache-control directive, or in
+   any request:
+      - Content-Encoding
+      - Content-Range
+      - Content-Type
-   A cache or non-caching
+   A non-transparent
proxy MAY modify or add these fields
-   in a response
+   to a message
that does not include no-transform, but if it does so, it MUST add a
-   Warning 14
+   Warning 214
(Transformation applied) if one does not already appear in the
-   response.
+   message (see section 14.46).
-
Warning: unnecessary modification of end-to-end headers
-     may
+      might
cause authentication failures if stronger authentication mechanisms are
introduced in later versions of HTTP. Such authentication
-     mechanisms may
+      mechanisms MAY
rely on the values of header fields not listed here.
+
+   The Content-Length field of a request or response is added or deleted
+   according to the rules in section 4.4. A transparent proxy MUST
+   preserve the entity-length (section 7.2.2) of the entity-body,
+   although it MAY change the transfer-length (section 4.4).
 
 13.5.3 Combining Headers
 
    When a cache makes a validating request to a server, and the server
-   provides a 304 (Not Modified) response,
+   provides a 304 (Not Modified) response or a 206 (Partial Content)
+   response,
-   the cache must construct a response to send to the requesting client.
+   the cache then constructs a response to send to the requesting client.

-   The cache uses the entity-body stored in the cache entry as the entity-body of this
-   outgoing response. The end-to-end headers stored in the cache entry
-   are used for the constructed response, except that any end-to-end
-   headers provided in the 304 response MUST replace the corresponding
-   headers from the cache entry. Unless the cache decides to remove the
-   cache entry, it MUST also replace the end-to-end headers stored with
-   the cache entry with corresponding headers received in the incoming
-   response.
+   If the status code is 304 (Not Modified), the cache uses the entity-body stored in the cache entry as the entity-body of this
+    outgoing response.
+   If the status code is 206 (Partial Content) and the ETag or
+   Last-Modified headers match exactly, the cache MAY combine the
+   contents stored in the cache entry with the new contents received in
+   the response and use the result as the entity-body of this outgoing
+   response, (see 13.5.4).
+
+   The end-to-end headers stored in the cache entry are used for the
+   constructed response, except that
+
+      - any stored Warning headers with warn-code 1xx (see section
+        14.46) MUST be deleted from the cache entry and the forwarded
+        response.
+
+      - any stored Warning headers with warn-code 2xx MUST be retained
+        in the cache entry and the forwarded response.
+
+      - any end-to-end headers provided in the 304 or 206 response MUST
+        replace the corresponding headers from the cache entry.
+
+   Unless the cache decides to remove the cache entry, it MUST also
+   replace the end-to-end headers stored with the cache entry with
+   corresponding headers received in the incoming response, except for
+   Warning headers as described immediately above. If a header field-
+   name in the incoming response matches more than one header in the
+   cache entry, all such old headers MUST be replaced.
 
    In other words, the set of end-to-end headers received in the
    incoming response overrides all corresponding end-to-end headers
-   stored with the cache entry. The cache may add Warning headers (see
+   stored with the cache entry (except for stored Warning headers with
-   section 14.45) to this set.
+   warn-code 1xx, which are deleted even if not overridden).
 
-   If a header field-name in the incoming response matches more than one
-   header in the cache entry, all such old headers are replaced.

Note: this rule allows an origin server to use a 304 (Not Modified)
+      or a 206 (Partial Content)
response to update any header associated with a previous response for the same entity
+       or sub-ranges thereof,
, although it might not always be meaningful or correct to do so.
This rule does not allow an origin server to use a 304
-      (not Modified)
+      (Not Modified) or a 206 (Partial Content)
response to entirely delete a header that it had provided with a previous response.
 
 13.5.4 Combining Byte Ranges
 
-   A response may transfer only a subrange of the bytes of an entity-
+   A response might transfer only a subrange of the bytes of an entity-
    body, either because the request included one or more Range
    specifications, or because a connection was broken prematurely. After
-   several such transfers, a cache may have received several ranges of
+   several such transfers, a cache might have received several ranges of
    the same entity-body.
 
    If a cache has a stored non-empty set of subranges for an entity, and
@@ -4188,64 +4462,80 @@
    combine the new subrange with the existing set if both the following
    conditions are met:
 
-     o  Both the incoming response and the cache entry must have a cache
+      - Both the incoming response and the cache entry have a cache
         validator.
-     o  The two cache validators must match using the strong comparison
+      - The two cache validators match using the strong comparison
         function (see section 13.3.3).
 
-   If either requirement is not meant, the cache must use only the most
+   If either requirement is not met, the cache MUST use only the most
    recent partial response (based on the Date values transmitted with
    every response, and using the incoming response if these values are
-   equal or missing), and must discard the other partial information.
+   equal or missing), and MUST discard the other partial information.
 
 13.6 Caching Negotiated Responses
 
-   Use of server-driven content negotiation (section 12), as indicated
+   Use of server-driven content negotiation (section 12.1), as indicated
    by the presence of a Vary header field in a response, alters the
    conditions and procedure by which a cache can use the response for
subsequent requests.
+   See section 14.44 for use of the Vary header
+   field by servers.
+
-   A server MUST use the Vary header field (section 14.43)
+   A server SHOULD use the Vary header field
-   to inform a cache of what header field dimensions are
+   to inform a cache of what request-header fields were
-   used to select among multiple representations of a cachable response.
+   used to select among multiple representations of a cacheable response subject to server-driven negotiation.
-   A cache may use the selected representation (the entity included with that particular
-   response) for replying to subsequent requests on that resource only
-   when the subsequent requests have the same or equivalent values for
-   all header fields specified in the Vary response-header. Requests
-   with a different value for one or more of those header fields would
-   be forwarded toward the origin server.
+   The set of header fields named by the Vary field value
+   is known as the "selecting" request-headers.
+
+   When the cache receives a subsequent request whose Request-URI
+   specifies one or more cache entries including a Vary header field,
+   the cache MUST NOT use such a cache entry to construct a response to
+   the new request unless all of the selecting request-headers present
+   in the new request match the corresponding stored request-headers in
+   the original request.
+
+   The selecting request-headers from two requests are defined to match
+   if and only if the selecting request-headers in the first request can
+   be transformed to the selecting request-headers in the second request
+   by adding or removing linear white space (LWS) at places where this
+   is allowed by the corresponding BNF, and/or combining multiple
+   message-header fields with the same field name following the rules
+   about message headers in section 4.2.

+   A Vary header field-value of "*" always fails to match and subsequent
+   requests on that resource can only be properly interpreted by the
+   origin server.
+
+   If the selecting request header fields for the cached entry do not
+   match the selecting request header fields of the new request, then
+   the cache MUST NOT use a cached entry to satisfy the request unless
+   it first relays the new request to the origin server in a conditional
+   request and the server responds with 304 (Not Modified), including an
+   entity tag or Content-Location that indicates the entity to be used.

If an entity tag was assigned to [DEL[the]] [INS[a cached]] representation, the forwarded
request SHOULD be conditional and include the entity tags in an If-None-Match header field from all its cache entries for the [DEL[Request-URI]] [INS[resource]]. This conveys to the server the set of entities currently held by
the cache, so that if any one of these entities matches the requested
entity, the server can use the ETag header in its 304 (Not Modified)
response to tell the cache which entry is appropriate. If the
entity-tag of the new response matches that of an existing entry, the
new response SHOULD be used to update the header fields of the
existing entry, and the result MUST be returned to the client.

-   The Vary header field may also inform the cache that the
-   representation was selected using criteria not limited to the
-   request-headers; in this case, a cache MUST NOT use the response in a
-   reply to a subsequent request unless the cache relays the new request
-   to the origin server in a conditional request and the server responds
-   with 304 (Not Modified), including an entity tag or Content-Location
-   that indicates which entity should be used.
 
    If any of the existing cache entries contains only partial content
    for the associated entity, its entity-tag SHOULD NOT be included in the If-None-Match header
+   field
unless the request is for a range that would be fully satisfied by that entry.
 
    If a cache receives a successful response whose Content-Location
    field matches that of an existing cache entry for the same Request-
-   URI, whose entity-tag differs from that of the existing entry, and
+   ]URI, whose entity-tag differs from that of the existing entry, and
    whose Date is more recent than that of the existing entry, the
-   existing entry SHOULD NOT be returned in response to future requests,
+   existing entry SHOULD NOT be returned in response to future requests
-   and should be deleted from the cache.
+   and SHOULD be deleted from the cache.
 
 13.7 Shared and Non-Shared Caches
 
@@ -4254,6 +4544,7 @@
    cache is one that is accessible only to a single user. Accessibility
    in this case SHOULD be enforced by appropriate security mechanisms.
    All other caches are considered to be "shared." Other sections of
+
    this specification place certain constraints on the operation of
    shared caches in order to prevent loss of privacy or failure of
    access controls.
@@ -4261,9 +4552,9 @@
 13.8 Errors or Incomplete Response Cache Behavior
 
    A cache that receives an incomplete response (for example, with fewer
-   bytes of data than specified in a Content-Length header) may store
+   bytes of data than specified in a Content-Length header) MAY store
    the response. However, the cache MUST treat this as a partial
-   response.  Partial responses may be combined as described in section
+   response. Partial responses MAY be combined as described in section
    13.5.4; the result might be a full response or might still be
    partial. A cache MUST NOT return a partial response to a client
    without explicitly marking it as such, using the 206 (Partial
@@ -4271,11 +4562,10 @@
    using a status code of 200 (OK).
 
    If a cache receives a 5xx response while attempting to revalidate an
-   entry, it may either forward this response to the requesting client,
+   entry, it MAY either forward this response to the requesting client,
    or act as if the server failed to respond. In the latter case, it MAY
    return a previously received response unless the cached entry
-   includes the "must-revalidate" Cache-Control directive (see section
+   includes the "must-revalidate" cache-control directive (see section
    14.9).
 
 13.9 Side Effects of GET and HEAD
@@ -4283,7 +4573,7 @@
    Unless the origin server explicitly prohibits the caching of their
    responses, the application of GET and HEAD methods to any resources
    SHOULD NOT have side effects that would lead to erroneous behavior if
-   these responses are taken from a cache. They may still have side
+   these responses are taken from a cache. They MAY still have side
    effects, but a cache is not required to consider such side effects in
    its caching decisions. Caches are always expected to observe an
    origin server's explicit restrictions on caching.
@@ -4291,53 +4581,59 @@
    We note one exception to this rule: since some applications have
    traditionally used GETs and HEADs with query URLs (those containing a
    "?" in the rel_path part) to perform operations with significant side
-   effects, caches MUST NOT treat responses to such URLs as fresh unless
+   effects, caches MUST NOT treat responses to such URIs as fresh unless
    the server provides an explicit expiration time. This specifically
-   means that responses from HTTP/1.0 servers for such URIs should not
+   means that responses from HTTP/1.0 servers for such URIs SHOULD NOT
    be taken from a cache. See section 9.1.1 for related information.
 
 13.10 Invalidation After Updates or Deletions
 
-   The effect of certain methods at the origin server may
+   The effect of certain methods performed on a resource at the origin server might
-   cause one or more existing cache entries to become non-transparently invalid.
+   cause one or more existing cache entries to become non-transparently invalid.
-   That is, although they may
+    That is, although they might
continue to be "fresh," they do not accurately reflect what the origin server would return for a new request
+   on that resource
.
 
    There is no way for the HTTP protocol to guarantee that all such
    cache entries are marked invalid. For example, the request that
-   caused the change at the origin server may not have gone through
+   caused the change at the origin server might not have gone through
the proxy where a cache entry is stored. However, several rules help
    reduce the likelihood of erroneous behavior.
 
    In this section, the phrase "invalidate an entity" means that the
-   cache should either remove all instances of that entity from its
+   cache will either remove all instances of that entity from its
-   storage, or should mark these as "invalid" and in need of a mandatory
+   storage, or will mark these as "invalid" and in need of a mandatory
    revalidation before they can be returned in response to a subsequent
    request.
 
-   Some HTTP methods may invalidate an entity.
+   Some HTTP methods MUST cause a cache to invalidate an entity.
This is either the entity referred to by the Request-URI, or by the Location
-    or Content-Location response-headers (if present). These methods are:
+   or Content-Location headers (if present). These methods are:
 
-
-     o  PUT
-     o  DELETE
-     o  POST
+      - PUT
+
+      - DELETE
+
+      - POST
 
    [DEL[In order to prevent denial of service attacks, an]] [INA[An]] invalidation based
    on the URI in a Location or Content-Location header MUST [DEL[only]] [INS[NOT]] be
    performed if the host part [DEL[is the same as]]
    [INS[of that URI differs from the host part]] in the Request-URI.
    [INS[This helps prevent denial of service attacks.]]
    [INS[{ammended by errata}]]
 
+   A cache that passes through requests for methods it does not
+   understand SHOULD invalidate any entities referred to by the
+   Request-URI.
+
 13.11 Write-Through Mandatory
 
-   All methods that may be expected to cause modifications to the
+   All methods that might be expected to cause modifications to the
origin server's resources MUST be written through to the origin server. This
currently includes all methods except for GET and HEAD. A cache MUST
NOT reply to such a request from a client before having transmitted
the request to the inbound server, and having received a
corresponding response from the inbound server. This does not prevent
-   a cache from sending a 100 (Continue) response before the
+   a proxy cache from sending a 100 (Continue) response before the
-   inbound server has replied.
+   inbound server has sent its final reply.
 
    The alternative (known as "write-back" or "copy-back" caching) is not
    allowed in HTTP/1.1, due to the difficulty of providing consistent
@@ -4346,17 +4642,17 @@
 
 13.12 Cache Replacement
 
-   If a new cachable (see sections 14.9.2, 13.2.5, 13.2.6 and 13.8)
+   If a new cacheable (see sections 14.9.2, 13.2.5, 13.2.6 and 13.8)
    response is received from a resource while any existing responses for
    the same resource are cached, the cache SHOULD use the new response
-   to reply to the current request. It may insert it into cache storage
+   to reply to the current request. It MAY insert it into cache storage
-   and may, if it meets all other requirements, use it to respond to any
+   and MAY, if it meets all other requirements, use it to respond to any
    future requests that would previously have caused the old response to
be returned. If it inserts the new response into cache storage 
-   it should follow the rules in section 13.5.3.
+   the rules in section 13.5.3 apply.
 
Note: a new response that has an older Date header value than
-     existing cached responses is not cachable.
+      existing cached responses is not cacheable.
 
 13.13 History Lists
 
@@ -4371,24 +4667,25 @@
    retrieved.
 
    By default, an expiration time does not apply to history mechanisms.
-   If the entity is still in storage, a history mechanism should display
+   If the entity is still in storage, a history mechanism SHOULD display
    it even if the entity has expired, unless the user has specifically
    configured the agent to refresh expired history documents.
 
-   This should not be construed to prohibit the history mechanism from
+   This is not to be construed to prohibit the history mechanism from
-   telling the user that a view may be stale.
+   telling the user that a view might be stale.

Note: if history list mechanisms unnecessarily prevent users from
viewing stale resources, this will tend to force service authors
to avoid using HTTP expiration controls and cache controls when
they would otherwise like to. Service authors may consider it
important that users not be presented with error messages or warning
messages when they use navigation controls (such as BACK) to view
previously fetched resources. Even though sometimes such resources
ought not to cached, or ought to expire quickly, user interface
considerations may force service authors to resort to other means
of preventing caching (e.g. "once-only" URLs) in order not to
suffer the effects of improperly functioning history mechanisms.
 
 14 Header Field Definitions
 
@@ -4397,9 +4694,6 @@
    recipient refer to either the client or the server, depending on who
    sends and who receives the entity.

 14.1 Accept
 
    The Accept request-header field can be used to specify certain media
@@ -4408,17 +4702,15 @@
    set of desired types, as in the case of a request for an in-line
    image.
 
       Accept         = "Accept" ":"
                        #( media-range [ accept-params ] )

       media-range    = ( "*/*"
                        | ( type "/" "*" )
                        | ( type "/" subtype )
                        ) *( ";" parameter )
       accept-params  = ";" "q" "=" qvalue *( accept-extension )
       accept-extension = ";" token [ "=" ( token | quoted-string ) ]
 
    The asterisk "*" character is used to group media types into ranges,
    with "*/*" indicating all media types and "type/*" indicating all
@@ -4433,18 +4725,18 @@
    media-range, using the qvalue scale from 0 to 1 (section 3.9). The
    default value is q=1.
 
Note: Use of the "q" parameter name to separate media type
parameters from Accept extension parameters is due to historical
practice. Although this prevents any media type parameter named
"q" from being used with a media range, such an event is believed
to be unlikely given the lack of any "q" parameters in the IANA
media type registry and the rare usage of any media type
parameters in Accept. Future media types are discouraged from
registering any parameter named "q".
 
    The example
 
       Accept: audio/*; q=0.2, audio/basic
 
    SHOULD be interpreted as "I prefer audio/basic, but send me any audio
    type if it is the best available after an 80% mark-down in quality."
@@ -4457,8 +4749,8 @@
 
    A more elaborate example is
 
       Accept: text/plain; q=0.5, text/html,
               text/x-dvi; q=0.8, text/x-c
 
    Verbally, this would be interpreted as "text/html and text/x-c are
    the preferred media types, but if they do not exist, then send the
@@ -4469,36 +4761,36 @@
    specific media types. If more than one media range applies to a given
    type, the most specific reference has precedence. For example,
 
       Accept: text/*, text/html, text/html;level=1, */*
 
    have the following precedence:

       1) text/html;level=1
       2) text/html
       3) text/*
       4) */*
 
    The media type quality factor associated with a given type is
    determined by finding the media range with the highest precedence
    which matches that type. For example,
 
       Accept: text/*;q=0.3, text/html;q=0.7, text/html;level=1,
               text/html;level=2;q=0.4, */*;q=0.5
 
    would cause the following values to be associated:
 
       text/html;level=1         = 1
       text/html                 = 0.7
       text/plain                = 0.3
       image/jpeg                = 0.5
       text/html;level=2         = 0.4
       text/html;level=3         = 0.7

Note: A user agent might be provided with a default set of quality
values for certain media ranges. However, unless the user agent is
a closed system which cannot interact with other rendering agents,
this default set ought to be configurable by the user.
 
 14.2 Accept-Charset
 
@@ -4506,18 +4798,23 @@
    character sets are acceptable for the response. This field allows
    clients capable of understanding more comprehensive or special-
    purpose character sets to signal that capability to a server which is
capable of representing documents in those character sets.
-   The ISO-8859-1 character set can be assumed to be acceptable to all user
-   agents.
 
     Accept-Charset = "Accept-Charset" ":"
-                    1#( charset [ ";" "q" "=" qvalue ] )
+              1#( ( charset | "*" )[ ";" "q" "=" qvalue ] )
 
-   Character set values are described in section 3.4. Each charset may
+   Character set values are described in section 3.4. Each charset MAY
    be given an associated quality value which represents the user's
    preference for that charset. The default value is q=1. An example is
 
 Accept-Charset: iso-8859-5, unicode-1-1;q=0.8

+   The special value "*", if present in the Accept-Charset field,
+   matches every character set (including ISO-8859-1) which is not
+   mentioned elsewhere in the Accept-Charset field. If no "*" is present
+   in an Accept-Charset field, then all character sets not explicitly
+   mentioned get a quality value of 0, except for ISO-8859-1, which gets
+   a quality value of 1 if not explicitly mentioned.
 
    If no Accept-Charset header is present, the default is that any
    character set is acceptable. If an Accept-Charset header is present,
@@ -4529,42 +4826,85 @@
 14.3 Accept-Encoding
 
    The Accept-Encoding request-header field is similar to Accept, but restricts the 
-  content-coding values (section 14.12) which
+  content-codings (section 3.5) that
are acceptable in the response.
 
         Accept-Encoding  = "Accept-Encoding" ":"
-                                    #( content-coding )
+                          1#( codings [ ";" "q" "=" qvalue ] )
+       codings          = ( content-coding | "*" )
 
-   An example of its use is
+   Examples of its use are:
       Accept-Encoding: compress, gzip
+       Accept-Encoding:
+       Accept-Encoding: *
+       Accept-Encoding: compress;q=0.5, gzip;q=1.0
+       Accept-Encoding: gzip;q=1.0, identity; q=0.5, *;q=0

+   A server tests whether a content-coding is acceptable, according to
+   an Accept-Encoding field, using these rules:
+
+      1. If the content-coding is one of the content-codings listed in
+         the Accept-Encoding field, then it is acceptable, unless it is
+         accompanied by a qvalue of 0. (As defined in section 3.9, a
+         qvalue of 0 means "not acceptable.")
+
+      2. The special "*" symbol in an Accept-Encoding field matches any
+         available content-coding not explicitly listed in the header
+         field.
+
+      3. If multiple content-codings are acceptable, then the acceptable
+         content-coding with the highest non-zero qvalue is preferred.
+
+      4. The "identity" content-coding is always acceptable, unless
+         specifically refused because the Accept-Encoding field includes
+         "identity;q=0", or because the field includes "*;q=0" and does
+         not explicitly include the "identity" content-coding. If the
+         Accept-Encoding field-value is empty, then only the "identity"
+         encoding is acceptable.
+
+   If an Accept-Encoding field is present in a request, and if the
+   server cannot send a response which is acceptable according to the
+   Accept-Encoding header, then the server SHOULD send an error response
+   with the 406 (Not Acceptable) status code.
+
   If no Accept-Encoding field is present in a request, the server MAY
   assume that the client will accept any content coding.
+  In this case,
+   if "identity" is one of the available content-codings, then the
+   server SHOULD use the "identity" content-coding, unless it has
+   additional information that a different content-coding is meaningful
+   to the client.
- If an Accept-Encoding header is present, and if the server cannot send a response
-   which is acceptable according to the Accept-Encoding header, then the
-   server SHOULD send an error response with the 406 (Not Acceptable)
-   status code.
-
-   An empty Accept-Encoding value indicates none are acceptable.
+
+      Note: If the request does not include an Accept-Encoding field,
+      and if the "identity" content-coding is unavailable, then
+      content-codings commonly understood by HTTP/1.0 clients (i.e.,
+      "gzip" and "compress") are preferred; some older clients
+      improperly display messages sent with other content-codings.  The
+      server might also make this decision based on information about
+      the particular user-agent or client.
+
+      Note: Most HTTP/1.0 applications do not recognize or obey qvalues
+      associated with content-codings. This means that qvalues will not
+      work and are not permitted with x-gzip or x-compress.
 
 14.4 Accept-Language
 
    The Accept-Language request-header field is similar to Accept, but
    restricts the set of natural languages that are preferred as a
   response to the request.
+   Language tags are defined in section 3.10.

          Accept-Language = "Accept-Language" ":"
                            1#( language-range [ ";" "q" "=" qvalue ] )
 
       language-range  = ( ( 1*8ALPHA *( "-" 1*8ALPHA ) ) | "*" )
 
    Each language-range MAY be given an associated quality value which
    represents an estimate of the user's preference for the languages
    specified by that range. The quality value defaults to "q=1". For
    example,
 
Accept-Language: da, en-gb;q=0.8, en;q=0.7
 
    would mean: "I prefer Danish, but will accept British English and
    other types of English." A language-range matches a language-tag if
@@ -4574,146 +4914,161 @@
    matches every tag not matched by any other range present in the
    Accept-Language field.
 
Note: This use of a prefix matching rule does not imply that
language tags are assigned to languages in such a way that it is
always true that if a user understands a language with a certain
tag, then this user will also understand all languages with tags
for which this tag is a prefix. The prefix rule simply allows the
use of prefix tags if this is the case.
 
    The language quality factor assigned to a language-tag by the
    Accept-Language field is the quality value of the longest language-
    range in the field that matches the language-tag. If no language-
    range in the field matches the tag, the language quality factor
    assigned is 0. If no Accept-Language header is present in the
  request, the server SHOULD assume that all languages are equally
   acceptable. If an Accept-Language header is present, then all
   languages which are assigned a quality factor greater than 0 are
   acceptable.
 
-   It may be contrary to the privacy expectations of the user to send an
+   It might be contrary to the privacy expectations of the user to send an
   Accept-Language header with the complete linguistic preferences of
    the user in every request. For a discussion of this issue, see
-   section 15.7.
+   section 15.1.4.
 
-     Note:
As intelligibility is highly dependent on the individual
user, it is recommended that client applications make the choice of
linguistic preference available to the user. If the choice is not
made available, then the Accept-Language header field
-must not
+MUST NOT
be given in the request.
 
+      Note: When making the choice of linguistic preference available to
+      the user, we remind implementors of  the fact that users are not
+      familiar with the details of language matching as described above,
+      and should provide appropriate guidance. As an example, users
+      might assume that on selecting "en-gb", they will be served any
+      kind of English document if British English is not available. A
+      user agent might suggest in such a case to add "en" to get the
+      best matching behavior.
 
 14.5 Accept-Ranges
 
The Accept-Ranges response-header field allows the server to
indicate its acceptance of range requests for a resource:
 
           Accept-Ranges     = "Accept-Ranges" ":" acceptable-ranges
           acceptable-ranges = 1#range-unit | "none"
 
Origin servers that accept byte-range requests MAY send
 
           Accept-Ranges: bytes
 
but are not required to do so. Clients MAY generate byte-range
requests without having received this header for the resource
involved.
+ Range units are defined in section 3.12.

Servers that do not accept any kind of range request for a
resource MAY send
 
           Accept-Ranges: none
 
to advise the client not to attempt a range request.
 
 14.6 Age
 
The Age response-header field conveys the sender's estimate of the
amount of time since the response (or its revalidation) was generated
at the origin server. A cached response is "fresh" if its age does
not exceed its freshness lifetime. Age values are calculated as
specified in section 13.2.3.
 
            Age = "Age" ":" age-value
            age-value = delta-seconds
 
Age values are non-negative decimal integers, representing time in
seconds.
 
If a cache receives a value larger than the largest positive
integer it can represent, or if any of its age calculations
overflows, it MUST transmit an Age header with a value of
2147483648 (2^31).
-   HTTP/1.1 caches MUST send an Age header in every response.
+ An HTTP/1.1 server that includes a cache MUST
+      include an Age header field in every response generated from its
+      own cache.
Caches SHOULD use an arithmetic type of at least 31
bits of range.
 
 14.7 Allow
 
       The Allow entity-header field lists the set of methods supported
       by the resource identified by the Request-URI. The purpose of this
       field is strictly to inform the recipient of valid methods
       associated with the resource. An Allow header field MUST be
       present in a 405 (Method Not Allowed) response.
 
-          Allow          = "Allow" ":" 1#method
+          Allow   = "Allow" ":" #Method
 
-   Example of use:
+      Example of use:
 
           Allow: GET, HEAD, PUT
 
       This field cannot prevent a client from trying other methods.
       However, the indications given by the Allow header field value
       SHOULD be followed. The actual set of allowed methods is defined
       by the origin server at the time of each request.

       The Allow header field MAY be provided with a PUT request to
       recommend the methods to be supported by the new or modified
       resource. The server is not required to support these methods and
       SHOULD include an Allow header in the response giving the actual
       supported methods.

-   A proxy MUST NOT modify the Allow header field even if it does not
-   understand all the methods specified, since the user agent MAY have
-   other means of communicating with the origin server.
+      A proxy MUST NOT modify the Allow header field even if it does not
+      understand all the methods specified, since the user agent might
+      have other means of communicating with the origin server.
 
-   The Allow header field does not indicate what methods are implemented
-   at the server level. Servers MAY use the Public response-header field
-   (section 14.35) to describe what methods are implemented on the
-   server as a whole.

 
 14.8 Authorization
 
A user agent that wishes to authenticate itself with a server--
usually, but not necessarily, after receiving a 401 response--
-MAY do
+ does
so by including an Authorization request-header field with the
request. The Authorization field value consists of credentials
containing the authentication information of the user agent for the
realm of the resource being requested.
 
           Authorization  = "Authorization" ":" credentials
 
-   HTTP access authentication is described in section 11.
+      HTTP access authentication is described in "HTTP Authentication:
+      Basic and Digest Access Authentication" [43].
If a request is
authenticated and a realm specified, the same credentials SHOULD
be valid for all other requests within this realm
+(assuming that
+      the authentication scheme itself does not require otherwise, such
+      as credentials that vary according to a challenge value or using
+      synchronized clocks)
.

When a shared cache (see section 13.7) receives a request containing
an Authorization field, it MUST NOT return the corresponding response
as a reply to any other request, unless one of the following specific
exceptions holds:

-     1. If the response includes the "proxy-revalidate" Cache-Control
+      1. If the response includes the "s-maxage" cache-control
directive, the cache MAY use that response in replying to a
-        subsequent request, but
+         subsequent request. But (if the specified maximum age has
+         passed)
a proxy cache MUST first revalidate it with the origin
server, using the request-headers from the new request
to allow the origin server to authenticate the new request.
+        (This is the defined behavior for s-maxage.) If the response includes 
+         "s-maxage=0", the proxy MUST always revalidate it before re-using it.
2. If the response includes the "must-revalidate" 
-Cache-Control
+ cache-control
directive, the cache MAY use that response in replying to a subsequent request
-, but
+. But if the response is stale, 
all caches MUST first revalidate it with
the origin server, using the request-headers from the new request
to allow the origin server to authenticate the new request.
3. If the response includes the "public" 
-Cache-Control 
+cache-control
directive, it
-        may
+MAY
be returned in reply to any subsequent request.

 14.9 Cache-Control
 
@@ -4723,190 +5078,252 @@
    prevent caches from adversely interfering with the request or
    response. These directives typically override the default caching
    algorithms. Cache directives are unidirectional in that the presence
-   of a directive in a request does not imply that the same directive
-   should be given in the response.
+   of a directive in a request does not imply that the same directive is
+   to be given in the response.
 
-     Note that HTTP/1.0 caches may not implement Cache-Control and may
-     only implement Pragma: no-cache (see section 14.32).
+      Note that HTTP/1.0 caches might not implement Cache-Control and
+      might only implement Pragma: no-cache (see section 14.32).
 
-   Cache directives must be passed through by a proxy or gateway
+   Cache directives MUST be passed through by a proxy or gateway
    application, regardless of their significance to that application,
-   since the directives may be applicable to all recipients along the
+   since the directives might be applicable to all recipients along the
    request/response chain. It is not possible to specify a cache-
    directive for a specific cache.
 
-          Cache-Control   = "Cache-Control" ":" 1#cache-directive
+    Cache-Control   = "Cache-Control" ":" 1#cache-directive
 
-          cache-directive = cache-request-directive
-                          | cache-response-directive
+    cache-directive = cache-request-directive
+         | cache-response-directive
 
-          cache-request-directive =
-                            "no-cache" [ "=" <"> 1#field-name <"> ]
-                          | "no-store"
-                          | "max-age" "=" delta-seconds
-                          | "max-stale" [ "=" delta-seconds ]
-                          | "min-fresh" "=" delta-seconds
-                          | "only-if-cached"
-                          | cache-extension
+    cache-request-directive =
+           "no-cache"                          ; Section 14.9.1
+         | "no-store"                          ; Section 14.9.2
+         | "max-age" "=" delta-seconds         ; Section 14.9.3, 14.9.4
+         | "max-stale" [ "=" delta-seconds ]   ; Section 14.9.3
+         | "min-fresh" "=" delta-seconds       ; Section 14.9.3
+         | "no-transform"                      ; Section 14.9.5
+         | "only-if-cached"                    ; Section 14.9.4
+         | cache-extension                     ; Section 14.9.6
-
-          cache-response-directive =
-                            "public"
-                          | "private" [ "=" <"> 1#field-name <"> ]
-                          | "no-cache" [ "=" <"> 1#field-name <"> ]
-                          | "no-store"
-                          | "no-transform"
-                          | "must-revalidate"
-                          | "proxy-revalidate"
-                          | "max-age" "=" delta-seconds
-                          | cache-extension
+     cache-response-directive =
+           "public"                               ; Section 14.9.1
+         | "private" [ "=" <"> 1#field-name <"> ] ; Section 14.9.1
+         | "no-cache" [ "=" <"> 1#field-name <"> ]; Section 14.9.1
+         | "no-store"                             ; Section 14.9.2
+         | "no-transform"                         ; Section 14.9.5
+         | "must-revalidate"                      ; Section 14.9.4
+         | "proxy-revalidate"                     ; Section 14.9.4
+         | "max-age" "=" delta-seconds            ; Section 14.9.3
+         | "s-maxage" "=" delta-seconds           ; Section 14.9.3
+         | cache-extension                        ; Section 14.9.6
 
cache-extension = token [ "=" ( token | quoted-string ) ]
 
    When a directive appears without any 1#field-name parameter, the
    directive applies to the entire request or response. When such a
    directive appears with a 1#field-name parameter, it applies only to
    the named field or fields, and not to the rest of the request or
   response. This mechanism supports extensibility; implementations of
-   future versions of the HTTP protocol may apply these directives to
+   future versions of the HTTP protocol might apply these directives to
    header fields not defined in HTTP/1.1.
 
    The cache-control directives can be broken down into these general
    categories:
 
-     o  Restrictions on what is cachable; these may only be imposed by the
-        origin server.
+      - Restrictions on what are cacheable; these may only be imposed by
+        the origin server.
-     o  Restrictions on what may be stored by a cache; these may be imposed
-        by either the origin server or the user agent.
+      - Restrictions on what may be stored by a cache; these may be
+        imposed by either the origin server or the user agent.
-     o  Modifications of the basic expiration mechanism; these may be
+      - Modifications of the basic expiration mechanism; these may be
         imposed by either the origin server or the user agent.
-     o  Controls over cache revalidation and reload; these may only be
+      - Controls over cache revalidation and reload; these may only be
         imposed by a user agent.
-     o  Control over transformation of entities.
+      - Control over transformation of entities.
-     o  Extensions to the caching system.
+      - Extensions to the caching system.
 
-14.9.1 What is Cachable
+14.9.1 What is Cacheable
 
By default, a response is 
-cachable
+cacheable
if the requirements of the
request method, request header fields, and the response status
indicate that it is 
-cachable
+cacheable
. Section 13.4 summarizes these defaults for
-   cachability.
+   cacheability.
The following Cache-Control response directives allow an
origin server to override the default 
-cachability 
+cacheability 
of a response:

public
Indicates that the response [DEL[is cachable]] [INS[MAY be cached]] by any cache, even if it
would normally be [DEL[non-cachable or cachable]] [INS[non-cacheable or cacheable]] only within a non-shared
cache. (See also Authorization, section 14.8, for additional details.)

private
Indicates that all or part of the response message is intended for a
single user and MUST NOT be cached by a shared cache. This allows an
origin server to state that the specified parts of the response are
intended for only one user and are not a valid response for requests
by other users. A private (non-shared) cache 
-may cache the response.
+      MAY cache the response.

Note: This usage of the word private only controls where the
response may be cached, and cannot ensure the privacy of the
message content.

no-cache
-  Indicates that all or part of the response message MUST NOT be cached
-  anywhere.
+       If the no-cache directive does not specify a field-name, then a
+      cache MUST NOT use the response to satisfy a subsequent request
+      without successful revalidation with the origin server.
This allows an origin server to prevent caching even by caches that
have been configured to return stale responses to client requests.

+      If the no-cache directive does specify one or more field-names,
+      then a cache MAY use the response to satisfy a subsequent request,
+      subject to any other restrictions on caching. However, the
+      specified field-name(s) MUST NOT be sent in the response to a
+      subsequent request without successful revalidation with the origin
+      server. This allows an origin server to prevent the re-use of
+      certain header fields in a response, while still allowing caching
+      of the rest of the response.
 
Note: Most HTTP/1.0 caches will not recognize or obey this directive.

 14.9.2 What May be Stored by Caches
 
+   no-store
The purpose of the no-store directive is to prevent the inadvertent
release or retention of sensitive information (for example, on backup
tapes). The no-store directive applies to the entire message, and 
-may
+MAY
be sent either in a response or in a request. If sent in a request, a
cache MUST NOT store any part of either this request or any response
to it. If sent in a response, a cache MUST NOT store any part of
either this response or the request that elicited it. This directive
applies to both non-shared and shared caches. "MUST NOT store" in
this context means that the cache MUST NOT intentionally store the
information in non-volatile storage, and MUST make a best-effort
attempt to remove the information from volatile storage as promptly
as possible after forwarding it.

Even when this directive is associated with a response, users 
-may
+might
explicitly store such a response outside of the caching system (e.g.,
with a "Save As" dialog). History buffers 
-may 
+MAY
store such responses as part of their normal operation.

The purpose of this directive is to meet the stated requirements of
certain users and service authors who are concerned about accidental
releases of information via unanticipated accesses to cache data
structures. While the use of this directive 
-may 
+might
improve privacy in some cases, we caution that it is NOT in any way a reliable or
sufficient mechanism for ensuring privacy. In particular, malicious
or compromised caches 
-may
+might
not recognize or obey this directive
-;
+, 
and communications networks 
-may 
+might
be vulnerable to eavesdropping.

 14.9.3 Modifications of the Basic Expiration Mechanism
 
-   The expiration time of an entity may be specified by the origin
+   The expiration time of an entity MAY be specified by the origin
    server using the Expires header (see section 14.21). Alternatively,
-   it may be specified using the max-age directive in a response.
+   it MAY be specified using the max-age directive in a response. When
+   the max-age cache-control directive is present in a cached response,
+   the response is stale if its current age is greater than the age
+   value given (in seconds) at the time of a new request for that
+   resource. The max-age directive on a response implies that the
+   response is cacheable (i.e., "public") unless some other, more
+   restrictive cache directive is also present.
 
    If a response includes both an Expires header and a max-age
    directive, the max-age directive overrides the Expires header, even
    if the Expires header is more restrictive. This rule allows an origin
    server to provide, for a given response, a longer expiration time to
-   an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This may be
+   an HTTP/1.1 (or later) cache than to an HTTP/1.0 cache. This might be
    useful if certain HTTP/1.0 caches improperly calculate ages or
    expiration times, perhaps due to desynchronized clocks.
 
+   Many HTTP/1.0 cache implementations will treat an Expires value that
+   is less than or equal to the response Date value as being equivalent
+   to the Cache-Control response directive "no-cache". If an HTTP/1.1
+   cache receives such a response, and the response does not include a
+   Cache-Control header field, it SHOULD consider the response to be
+   non-cacheable in order to retain compatibility with HTTP/1.0 servers.
+
+       Note: An origin server might wish to use a relatively new HTTP
+       cache control feature, such as the "private" directive, on a
+       network including older caches that do not understand that
+       feature. The origin server will need to combine the new feature
+       with an Expires field whose value is less than or equal to the
+       Date value. This will prevent older caches from improperly
+       caching the response.
+
+   s-maxage
+       If a response includes an s-maxage directive, then for a shared
+       cache (but not for a private cache), the maximum age specified by
+       this directive overrides the maximum age specified by either the
+       max-age directive or the Expires header. The s-maxage directive
+       also implies the semantics of the proxy-revalidate directive (see
+       section 14.9.4), i.e., that the shared cache must not use the
+       entry after it becomes stale to respond to a subsequent request
+       without first revalidating it with the origin server. The s-
+       maxage directive is always ignored by a private cache.
+
-     Note: most older caches, not compliant with this specification,
+   Note that most older caches, not compliant with this specification,
-     do not implement any Cache-Control directives.  An origin server
+   do not implement any cache-control directives. An origin server
-     wishing to use a Cache-Control directive that restricts, but does not
+   wishing to use a cache-control directive that restricts, but does not
-     prevent, caching by an HTTP/1.1-compliant cache may exploit the
+   prevent, caching by an HTTP/1.1-compliant cache MAY exploit the
requirement that the max-age directive overrides the Expires header,
and the fact that pre-HTTP/1.1-compliant caches do not observe the
max-age directive.
 
-   Other directives allow an user agent to modify the basic expiration
-   mechanism. These directives may be specified on a request:
+   Other directives allow a user agent to modify the basic expiration
+   mechanism. These directives MAY be specified on a request:
 
    max-age
     Indicates that the client is willing to accept a response whose age
     is no greater than the specified time in seconds. Unless max-stale
     directive is also included, the client is not willing to accept a
     stale response.
 
    min-fresh
     Indicates that the client is willing to accept a response whose
     freshness lifetime is no less than its current age plus the
     specified time in seconds. That is, the client wants a response
     that will still be fresh for at least the specified number of
     seconds.
 
    max-stale
     Indicates that the client is willing to accept a response that has
     exceeded its expiration time. If max-stale is assigned a value,
     then the client is willing to accept a response that has exceeded
     its expiration time by no more than the specified number of
     seconds. If no value is assigned to max-stale, then the client is
     willing to accept a stale response of any age.
 
    If a cache returns a stale response, either because of a max-stale
    directive on a request, or because the cache is configured to
    override the expiration time of a response, the cache MUST attach a
-   Warning header to the stale response, using Warning 10 (Response is
+   Warning header to the stale response, using Warning 110 (Response is
    stale).
 
+   A cache MAY be configured to return stale responses without
+   validation, but only if this does not conflict with any "MUST"-level
+   requirements concerning cache validation (e.g., a "must-revalidate"
+   cache-control directive).
+
+   If both the new request and the cached entry include "max-age"
+   directives, then the lesser of the two values is used for determining
+   the freshness of the cached entry for that request.
+
 14.9.4 Cache Revalidation and Reload Controls
 
-   Sometimes an user agent may want or need to insist that a cache
+   Sometimes a user agent might want or need to insist that a cache
    revalidate its cache entry with the origin server (and not just with
    the next cache along the path to the origin server), or to reload its
-   cache entry from the origin server. End-to-end revalidation may be
+   cache entry from the origin server. End-to-end revalidation might be
    necessary if either the cache or the origin server has overestimated
    the expiration time of the cached response. End-to-end reload may be
    necessary if the cache entry has become corrupted for some reason.
@@ -4921,166 +5338,174 @@
    Control request directives:
 
    End-to-end reload
-     The request includes a "no-cache" Cache-Control directive or, for
+      The request includes a "no-cache" cache-control directive or, for
-     compatibility with HTTP/1.0 clients, "Pragma: no-cache". No field
+      compatibility with HTTP/1.0 clients, "Pragma: no-cache". Field
-     names may be included with the no-cache directive in a
+      names MUST NOT be included with the no-cache directive in a
request. The server MUST NOT use a cached copy when responding to
such a request.
 
    Specific end-to-end revalidation
-     The request includes a "max-age=0" Cache-Control directive, which
+      The request includes a "max-age=0" cache-control directive, which
     forces each cache along the path to the origin server to revalidate
     its own entry, if any, with the next cache or server. The initial
     request includes a cache-validating conditional with the client's
     current validator.
 
    Unspecified end-to-end revalidation
-     The request includes "max-age=0" Cache-Control directive, which
+      The request includes "max-age=0" cache-control directive, which
    forces each cache along the path to the origin server to revalidate
     its own entry, if any, with the next cache or server. The initial
     request does not include a cache-validating conditional; the first
     cache along the path (if any) that holds a cache entry for this
     resource includes a cache-validating conditional with its current
     validator.

+   max-age
When an intermediate cache is forced, by means of a max-age=0
directive, to revalidate its own cache entry, and the client has
supplied its own validator in the request, the supplied validator 
-may
+might
   differ from the validator currently stored with the cache entry. In
   this case, the cache 
-may
+MAY 
use either validator in making its own
   request without affecting semantic transparency.

However, the choice of validator may affect performance. The best
   approach is for the intermediate cache to use its own validator when
   making its request. If the server replies with 304 (Not Modified),
   then the cache should return its now validated copy to the client
   with a 200 (OK) response. If the server replies with a new entity and
   cache validator, however, the intermediate cache 
-should
+can
compare the returned validator with the one provided in the client's request,
using the strong comparison function. If the client's validator is
equal to the origin server's, then the intermediate cache simply
returns 304 (Not Modified). Otherwise, it returns the new entity with
a 200 (OK) response.

If a request includes the no-cache directive, it 
-   should not
+   SHOULD NOT
include min-fresh, max-stale, or max-age.
+      include min-fresh, max-stale, or max-age.

+   only-if-cached
In some cases, such as times of extremely poor network connectivity,
a client may want a cache to return only those responses that it
currently has stored, and not to reload or revalidate with the origin
server. To do this, the client may include the only-if-cached
directive in a request. If it receives this directive, a cache SHOULD
either respond using a cached entry that is consistent with the other
constraints of the request, or respond with a 504 (Gateway Timeout)
status. However, if a group of caches is being operated as a unified
system with good internal connectivity, such a request MAY be
forwarded within that group of caches.

+   must-revalidate
Because a cache [DEL[may]] [INS[MAY]] be configured to ignore a server's specified
expiration time, and because a client request [DEL[may]] [INS[MAY]] include a max-stale
directive (which has a similar effect), the protocol also includes a
mechanism for the origin server to require revalidation of a cache
entry on any subsequent use. When the must-revalidate directive is
present in a response received by a cache, that cache MUST NOT use
the entry after it becomes stale to respond to a subsequent request
without first revalidating it with the origin server. (I.e., the
cache [DEL[must]] [INS[MUST]] do an end-to-end revalidation every time, if, based solely
on the origin server's Expires or max-age value, the cached response is stale.)

The must-revalidate directive is necessary to support reliable
operation for certain protocol features. In all circumstances an
HTTP/1.1 cache MUST obey the must-revalidate directive; in
particular, if the cache cannot reach the origin server for any
reason, it MUST generate a 504 (Gateway Timeout) response.

Servers [DEL[should]] [INS[SHOULD]] send the must-revalidate directive if and only if
failure to revalidate a request on the entity could result in
incorrect operation, such as a silently unexecuted financial
transaction.  Recipients MUST NOT take any automated action that
violates this directive, and MUST NOT automatically provide an
unvalidated copy of the entity if revalidation fails.

Although this is not recommended, user agents operating under severe
connectivity constraints [DEL[may]] [INS[MAY]] violate this directive but, if so, MUST
explicitly warn the user that an unvalidated response has been
provided.  The warning MUST be provided on each unvalidated access,
and SHOULD require explicit user confirmation.

+   proxy-revalidate
The proxy-revalidate directive has the same meaning as the must-revalidate
directive, except that it does not apply to non-shared
user agent caches. It can be used on a response to an authenticated
request to permit the user's cache to store and later return the
response without needing to revalidate it (since it has already been
authenticated once by that user), while still requiring proxies that
service many users to revalidate each time (in order to make sure
that each user has been authenticated). Note that such authenticated
responses also need the public cache control directive in order to
allow them to be cached at all.

 14.9.5 No-Transform Directive
 
+   no-transform
Implementers of intermediate caches (proxies) have found it useful to
convert the media type of certain entity bodies. A 
+      non-transparent
proxy might, for example, convert between image formats in order to save cache space
or to reduce the amount of traffic on a slow link. [DEL[HTTP has to date been silent on these transformations.]]

Serious operational problems [DEL[have already occurred]] [INS[occur]], however, when
these transformations [DEL[have been]] [INS[are]] applied to entity bodies intended for
certain kinds of applications. For example, applications for medical
imaging, scientific data analysis and those using end-to-end
authentication, all depend on receiving an entity body that is bit
for bit identical to the original entity-body.

Therefore, if a response includes the no-transform directive, an
intermediate cache or proxy MUST NOT change those headers that are
listed in section 13.5.2 as being subject to the no-transform
directive.  This implies that the cache or proxy 
-must not 
+MUST NOT 
change any aspect of the entity-body that is specified by these headers
-  .
+  , including the value of the entity-body itself.
 
 14.9.6 Cache Control Extensions
 
    The Cache-Control header field can be extended through the use of one
    or more cache-extension tokens, each with an optional assigned value.
    Informational extensions (those which do not require a change in
-   cache behavior) may be added without changing the semantics of other
+   cache behavior) MAY be added without changing the semantics of other
    directives. Behavioral extensions are designed to work by acting as
    modifiers to the existing base of cache directives. Both the new
    directive and the standard directive are supplied, such that
    applications which do not understand the new directive will default
    to the behavior specified by the standard directive, and those that
    understand the new directive will recognize it as modifying the
-   requirements associated with the standard directive.  In this way,
-   extensions to the Cache-Control directives can be made without
+   requirements associated with the standard directive. In this way,
+   extensions to the cache-control directives can be made without
    requiring changes to the base protocol.
 
-   This extension mechanism depends on a HTTP cache obeying all of the
+   This extension mechanism depends on an HTTP cache obeying all of the
    cache-control directives defined for its native HTTP-version, obeying
    certain extensions, and ignoring all directives that it does not
    understand.
 
    For example, consider a hypothetical new response directive called
-   "community" which acts as a modifier to the "private" directive. We
+   community which acts as a modifier to the private directive. We
    define this new directive to mean that, in addition to any non-shared
    cache, any cache which is shared only by members of the community
    named within its value may cache the response. An origin server
-   wishing to allow the "UCI" community to use an otherwise private
-   response in their shared cache(s) may do so by including
+   wishing to allow the UCI community to use an otherwise private
+   response in their shared cache(s) could do so by including
 
-          Cache-Control: private, community="UCI"
+       Cache-Control: private, community="UCI"
 
    A cache seeing this header field will act correctly even if the cache
-   does not understand the "community" cache-extension, since it will
-   also see and understand the "private" directive and thus default to
-   the safe behavior.
+   does not understand the community cache-extension, since it will also
+   see and understand the private directive and thus default to the safe
+   behavior.
 
    Unrecognized cache-directives MUST be ignored; it is assumed that any
    cache-directive likely to be unrecognized by an HTTP/1.1 cache will
    be combined with standard directives (or the response's default
-   cachability) such that the cache behavior will remain minimally
+   cacheability) such that the cache behavior will remain minimally
    correct even if the cache does not understand the extension(s).
 
 14.10 Connection
@@ -5091,8 +5516,8 @@
 
    The Connection header has the following grammar:
 
-          Connection-header = "Connection" ":" 1#(connection-token)
-          connection-token  = token
+       Connection = "Connection" ":" 1#(connection-token)
+       connection-token  = token
 
    HTTP/1.1 proxies MUST parse the Connection header field before a
    message is forwarded and, for each connection-token in this field,
@@ -5101,68 +5526,75 @@
    a connection-token in the Connection header field, not by any
    corresponding additional header field(s), since the additional header
    field may not be sent if there are no parameters associated with that
-   connection option.  HTTP/1.1 defines the "close" connection option
-   for the sender to signal that the connection will be closed after
-   completion of the response. For example,
+   connection option.
 
+   Message headers listed in the Connection header MUST NOT include
+   end-to-end headers, such as Cache-Control.
+
+   HTTP/1.1 defines the "close" connection option for the sender to
+   signal that the connection will be closed after completion of the
+   response. For example,
+
Connection: close
 
    in either the request or the response header fields indicates that
-   the connection should not be considered `persistent' (section 8.1)
+   the connection SHOULD NOT be considered `persistent' (section 8.1)
    after the current request/response is complete.
 
 [DEL[
    HTTP/1.1 applications that do not support persistent connections MUST
    include the "close" connection option in every message.
 ]DEL]
 [INS[{errata}]]
 [INS[
  An HTTP/1.1 client that does not support persistent connections MUST include the "close" connection option in every request message.

An HTTP/1.1 server that does not support persistent connections MUST include the "close" connection option in every response message that does not have a 1xx (informational) status code.
]INS]

+   A system receiving an HTTP/1.0 (or lower-version) message that
+   includes a Connection header MUST, for each connection-token in this
+   field, remove and ignore any header field(s) from the message with
+   the same name as the connection-token. This protects against mistaken
+   forwarding of such header fields by pre-HTTP/1.1 proxies. See section
+   19.6.2.

-14.11 Content-Base
-
-   The Content-Base entity-header field may be used to specify the base
-   URI for resolving relative URLs within the entity. This header field
-   is described as Base in RFC 1808, which is expected to be revised.
-
-          Content-Base      = "Content-Base" ":" absoluteURI
-
-   If no Content-Base field is present, the base URI of an entity is
-   defined either by its Content-Location (if that Content-Location URI
-   is an absolute URI) or the URI used to initiate the request, in that
-
-   order of precedence. Note, however, that the base URI of the contents
-   within the entity-body may be redefined within that entity-body.
 
-14.12 Content-Encoding
+14.11 Content-Encoding
 
    The Content-Encoding entity-header field is used as a modifier to the
    media-type. When present, its value indicates what additional content
    codings have been applied to the entity-body, and thus what decoding
-   mechanisms MUST be applied in order to obtain the media-type
+   mechanisms must be applied in order to obtain the media-type
    referenced by the Content-Type header field. Content-Encoding is
    primarily used to allow a document to be compressed without losing
    the identity of its underlying media type.
 
-          Content-Encoding  = "Content-Encoding" ":" 1#content-coding
+       Content-Encoding  = "Content-Encoding" ":" 1#content-coding
 
    Content codings are defined in section 3.5. An example of its use is
 
-          Content-Encoding: gzip
+       Content-Encoding: gzip
 
-   The Content-Encoding is a characteristic of the entity identified by
+   The content-coding is a characteristic of the entity identified by
    the Request-URI. Typically, the entity-body is stored with this
    encoding and is only decoded before rendering or analogous usage.
+   However, a non-transparent proxy MAY modify the content-coding if the
+   new coding is known to be acceptable to the recipient, unless the
+   "no-transform" cache-control directive is present in the message.
+
+   If the content-coding of an entity is not "identity", then the
+   response MUST include a Content-Encoding entity-header (section
+   14.11) that lists the non-identity content-coding(s) used.
+
+   If the content-coding of an entity in a request message is not
+   acceptable to the origin server, the server SHOULD respond with a
+   status code of 415 (Unsupported Media Type).
 
    If multiple encodings have been applied to an entity, the content
    codings MUST be listed in the order in which they were applied.
-
    Additional information about the encoding parameters MAY be provided
    by other entity-header fields not defined by this specification.
 
-14.13 Content-Language
+14.12 Content-Language
 
    The Content-Language entity-header field describes the natural
    language(s) of the intended audience for the enclosed entity. Note
-   that this may not be equivalent to all the languages used within the
-   entity-body.
+   that this might not be equivalent to all the languages used within
+   the entity-body.
 
-          Content-Language  = "Content-Language" ":" 1#language-tag
+       Content-Language  = "Content-Language" ":" 1#language-tag
 
    Language tags are defined in section 3.10. The primary purpose of
    Content-Language is to allow a user to identify and differentiate
@@ -5170,85 +5602,82 @@
    body content is intended only for a Danish-literate audience, the
    appropriate field is
 
-          Content-Language: da
+       Content-Language: da
 
    If no Content-Language is specified, the default is that the content
-   is intended for all language audiences. This may mean that the sender
+   is intended for all language audiences. This might mean that the sender
does not consider it to be specific to any natural language, or that
the sender does not know for which language it is intended.
 
    Multiple languages MAY be listed for content that is intended for
    multiple audiences. For example, a rendition of the "Treaty of
    Waitangi," presented simultaneously in the original Maori and English
    versions, would call for
 
Content-Language: mi, en
 
    However, just because multiple languages are present within an entity
    does not mean that it is intended for multiple linguistic audiences.
    An example would be a beginner's language primer, such as "A First
    Lesson in Latin," which is clearly intended to be used by an
-   English-literate audience. In this case, the Content-Language should
+   English-literate audience. In this case, the Content-Language would properly
only include "en".
 
-   Content-Language may be applied to any media type -- it is not
+   Content-Language MAY be applied to any media type -- it is not
    limited to textual documents.
 
-14.14 Content-Length
+14.13 Content-Length
 
    The Content-Length entity-header field indicates the size of the
-   message-body, in decimal number of octets, sent to the recipient or,
+   entity-body, in decimal number of OCTETs, sent to the recipient or,
    in the case of the HEAD method, the size of the entity-body that
    would have been sent had the request been a GET.
 
-          Content-Length    = "Content-Length" ":" 1*DIGIT
+       Content-Length    = "Content-Length" ":" 1*DIGIT
 
    An example is
 
-          Content-Length: 3495
+       Content-Length: 3495
 
-   Applications SHOULD use this field to indicate the size of the
-   message-body to be transferred, regardless of the media type of the
-   entity. It must be possible for the recipient to reliably determine
-   the end of HTTP/1.1 requests containing an entity-body, e.g., because
-   the request has a valid Content-Length field, uses Transfer-Encoding:
-   chunked or a multipart body.
+   Applications SHOULD use this field to indicate the transfer-length of
+   the message-body, unless this is prohibited by the rules in section
+   4.4.
 
    Any Content-Length greater than or equal to zero is a valid value.
    Section 4.4 describes how to determine the length of a message-body
    if a Content-Length is not given.
 
-     Note: The
+   Note that the 
meaning of this field is significantly different from the
corresponding definition in MIME, where it is an optional field
used within the "message/external-body" content-type. In HTTP, it
SHOULD be sent whenever the message's length can be determined prior
- .
+ , unless this is prohibited by the rules in section 4.4.
-
-14.15 Content-Location
+14.14 Content-Location
-
-   The Content-Location entity-header field may be used to supply the
+   The Content-Location entity-header field MAY be used to supply the
resource location for the entity enclosed in the message
-.
+   when that
+   entity is accessible from a location separate from the requested
+   resource's URI. A server SHOULD provide a Content-Location for the
+   variant corresponding to the response entity; especially in
- In
    the case where a resource has multiple entities associated with it, and those
    entities actually have separate locations by which they might be individually accessed, the server 
-  should 
+  SHOULD
provide a Content-Location for the particular variant which is returned.
-   In addition, a server SHOULD provide a Content-Location for the resource corresponding to the response entity.
+
Content-Location = "Content-Location" ":"
                         ( absoluteURI | relativeURI )
-
-   If no Content-Base header field is present, the value of Content-
-   Location also defines the base URL for the entity (see section
-   14.11).
+
+   The value of Content-Location also defines the base URI for the
+   entity.
 
    The Content-Location value is not a replacement for the original
    requested URI; it is only a statement of the location of the resource
    corresponding to this particular entity at the time of the request. Future requests MAY
-   use 
+   specify 
the Content-Location URI
+ as the request-URI
if the desire is to identify the source of that particular entity.
 
    A cache cannot assume that an entity with a Content-Location
    different from the URI used to retrieve it can be used to respond to
@@ -5257,13 +5686,13 @@
    retrieved from a single requested resource, as described in section
    13.6.
 
 If the Content-Location is a relative URI, the
+   relative
URI is interpreted relative to
-   any Content-Base URI provided in the response.
+   the Request-URI.
-   If no Content-Base is provided, the relative URI is interpreted relative to
-   the Request-URI.
 
+   The meaning of the Content-Location header in PUT or POST requests is
+   undefined; servers are free to ignore it in those cases.
 
-14.16 Content-MD5
+14.15 Content-MD5
 
    The Content-MD5 entity-header field, as defined in RFC 1864 [23], is
    an MD5 digest of the entity-body for the purpose of providing an
@@ -5271,108 +5700,114 @@
    MIC is good for detecting accidental modification of the entity-body
    in transit, but is not proof against malicious attacks.)
 
Content-MD5   = "Content-MD5" ":" md5-digest
md5-digest   = <base64 of 128 bit MD5 digest as per RFC 1864>
 
-   The Content-MD5 header field may be generated by an origin server to
+   The Content-MD5 header field MAY be generated by an origin server or client to
function as an integrity check of the entity-body. Only origin
-   servers may generate the Content-MD5 header field; proxies and
+   servers or clients MAY generate the Content-MD5 header field; proxies and
gateways MUST NOT generate it, as this would defeat its value as an
end-to-end integrity check. Any recipient of the entity-body,
including gateways and proxies, MAY check that the digest value in
this header field matches that of the entity-body as received.
 
    The MD5 digest is computed based on the content of the entity-body,
-   including any Content-Encoding that has been applied, but not
+   including any content-coding that has been applied, but not
-   including any Transfer-Encoding that may have been applied to the
+   including any transfer-encoding applied to the
-   message-body. If the message is received with a Transfer-Encoding,
+   message-body. If the message is received with a transfer-encoding,
-   that encoding must
+   that encoding MUST
be removed prior to checking the Content-MD5 value
 
    This has the result that the digest is computed on the octets of the
    entity-body exactly as, and in the order that, they would be sent if
-   no Transfer-Encoding were being applied.
+   no transfer-encoding were being applied.
 
    HTTP extends RFC 1864 to permit the digest to be computed for MIME
    composite media-types (e.g., multipart/* and message/rfc822), but
    this does not change how the digest is computed as defined in the
    preceding paragraph.
 
-     Note:
There are several consequences of this. The entity-body for composite types
-     may
+   MAY
contain many body-parts, each with its own MIME and HTTP
headers (including Content-MD5, Content-Transfer-Encoding, and
Content-Encoding headers). If a body-part has a Content-Transfer-Encoding
or Content-Encoding header, it is assumed that the content
of the body-part has had the encoding applied, and the body-part is
included in the Content-MD5 digest as is -- i.e., after the
application. The Transfer-Encoding header field is not allowed within
body-parts.
-
+   Conversion of all line breaks to CRLF MUST NOT be done before
+   computing or checking the digest: the line break convention used in
+   the text actually transmitted MUST be left unaltered when computing
+   the digest.

Note: while the definition of Content-MD5 is exactly the same for
HTTP as in RFC 1864 for MIME entity-bodies, there are several ways
in which the application of Content-MD5 to HTTP entity-bodies
differs from its application to MIME entity-bodies. One is that
HTTP, unlike MIME, does not use Content-Transfer-Encoding, and
does use Transfer-Encoding and Content-Encoding. Another is that
HTTP more frequently uses binary content types than MIME, so it is
worth noting that, in such cases, the byte order used to compute
the digest is the transmission byte order defined for the type.
Lastly, HTTP allows transmission of text types with any of several
line break conventions and not just the canonical form using CRLF.
-     Conversion of all line breaks to CRLF should not be done before
-     computing or checking the digest: the line break convention used in
-     the text actually transmitted should be left unaltered when
-     computing the digest.
 
-14.17 Content-Range
+14.16 Content-Range
 
    The Content-Range entity-header is sent with a partial entity-body to
    specify where in the full entity-body the partial body should be
-   inserted. It also indicates the total size of the full entity-body.
+   applied. Range units are defined in section 3.12.
-   When a server returns a partial response to a client, it must
-   describe both the extent of the range covered by the response, and
-   the length of the entire entity-body.
-
Content-Range = "Content-Range" ":" content-range-spec
content-range-spec      = byte-content-range-spec
-
-          byte-content-range-spec = bytes-unit SP first-byte-pos "-"
-                                    last-byte-pos "/" entity-length
+       byte-content-range-spec = bytes-unit SP
+                                 byte-range-resp-spec "/"
+                                 ( instance-length | "*" )
+       byte-range-resp-spec = (first-byte-pos "-" last-byte-pos)
+                                      | "*"
 
-          entity-length           = 1*DIGIT
+       instance-length           = 1*DIGIT
-
+   The header SHOULD indicate the total length of the full entity-body,
+   unless this length is unknown or difficult to determine. The asterisk
+   "*" character means that the instance-length is unknown at the time
+   when the response was generated.

-   Unlike byte-ranges-specifier values,
+   Unlike byte-ranges-specifier values (see section 14.35.1),
-   a byte-content-range-spec may 
+   a byte-range-resp-spec MUST 
only specify one range, and 
-must
+MUST
contain absolute byte positions for both the first and last byte of the range.
+  
-
A byte-content-range-spec 
+with a byte-range-resp-spec 
whose last-byte-pos value is less than its first-byte-pos value, or whose
-   entity-length value is less than or
+    instance-length value is less than or
equal to its last-byte-pos value, is invalid. The recipient of an
invalid byte-content-range-spec MUST ignore it and any content
transferred along with it.
+
+   A server sending a response with status code 416 (Requested range not
+   satisfiable) SHOULD include a Content-Range field with a byte-range-
+   resp-spec of "*". The instance-length specifies the current length of
+   the selected resource. A response with status code 206 (Partial
+   Content) MUST NOT include a Content-Range field with a byte-range-
+   resp-spec of "*".
 
    Examples of byte-content-range-spec values, assuming that the entity
    contains a total of 1234 bytes:
 
-     o  The first 500 bytes:
-          bytes 0-499/1234
+      . The first 500 bytes:
+       bytes 0-499/1234
-
-     o  The second 500 bytes:
-          bytes 500-999/1234
+      . The second 500 bytes:
+       bytes 500-999/1234
 
-     o  All except for the first 500 bytes:
-          bytes 500-1233/1234
+      . All except for the first 500 bytes:
+       bytes 500-1233/1234
 
-
-     o  The last 500 bytes:
-          bytes 734-1233/1234
+      . The last 500 bytes:
+       bytes 734-1233/1234
 
    When an HTTP message includes the content of a single range (for
    example, a response to a request for a single range, or to a request
@@ -5380,155 +5815,235 @@
    transmitted with a Content-Range header, and a Content-Length header
    showing the number of bytes actually transferred. For example,
 
       HTTP/1.1 206 Partial content
       Date: Wed, 15 Nov 1995 06:25:24 GMT
       Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
       Content-Range: bytes 21010-47021/47022
       Content-Length: 26012
       Content-Type: image/gif
 
    When an HTTP message includes the content of multiple ranges (for
    example, a response to a request for multiple non-overlapping
-   ranges), these are transmitted as a multipart MIME message. The multipart
+   ranges), these are transmitted as a multipart message. The multipart
-   MIME content-type used for this purpose is defined in this specification
+   media type used for this purpose is "multipart/byteranges" as defined
-   to be "multipart/byteranges". See appendix 19.2 for its definition.
+   in appendix 19.2. See appendix 19.6.3 for a compatibility issue.
-
-   A client that cannot decode a MIME multipart/byteranges message
-   should not ask for multiple byte-ranges in a single request.
+
+   A response to a request for a single range MUST NOT be sent using the
+   multipart/byteranges media type.  A response to a request for
+   multiple ranges, whose result is a single range, MAY be sent as a
+   multipart/byteranges media type with one part. A client that cannot
+   decode a multipart/byteranges message MUST NOT ask for multiple
+   byte-ranges in a single request.
 
    When a client requests multiple byte-ranges in one request, the
    server SHOULD return them in the order that they appeared in the
    request.
 
-   If the server ignores a byte-range-spec because it is invalid, the
+   If the server ignores a byte-range-spec because it is syntactically invalid, the
-   server should treat the request as if the invalid Range header field
+   server SHOULD treat the request as if the invalid Range header field
did not exist. (Normally, this means return a 200 response containing
the full entity).
-   The reason is that the only time a client will make
-   such an invalid request is when the entity is smaller than the entity
-   retrieved by a prior request.
+
+   If the server receives a request (other than one including an If-
+   Range request-header field) with an unsatisfiable Range request-
+   header field (that is, all of whose byte-range-spec values have a
+   first-byte-pos value greater than the current length of the selected
+   resource), it SHOULD return a response code of 416 (Requested range
+   not satisfiable) (section 10.4.17).
+
+      Note: clients cannot depend on servers to send a 416 (Requested
+      range not satisfiable) response instead of a 200 (OK) response for
+      an unsatisfiable Range request-header, since not all servers
+      implement this request-header.
 
-
-14.18 Content-Type
+14.17 Content-Type
 
    The Content-Type entity-header field indicates the media type of the
    entity-body sent to the recipient or, in the case of the HEAD method,
    the media type that would have been sent had the request been a GET.
 
Content-Type   = "Content-Type" ":" media-type
+
    Media types are defined in section 3.7. An example of the field is
 
Content-Type: text/html; charset=ISO-8859-4
 
    Further discussion of methods for identifying the media type of an
    entity is provided in section 7.2.1.
 
-14.19 Date
+14.18 Date
 
    The Date general-header field represents the date and time at which
    the message was originated, having the same semantics as orig-date in
    RFC 822. The field value is an HTTP-date, as described in section
-   3.3.1.
+   3.3.1; it MUST be sent in RFC 1123 [8]-date format.
 
Date  = "Date" ":" HTTP-date
 
    An example is
 
Date: Tue, 15 Nov 1994 08:12:31 GMT
 
-   If a message is received via direct connection with the user agent
-   (in the case of requests) or the origin server (in the case of
-   responses), then the date can be assumed to be the current date at
-   the receiving end. However, since the date--as it is believed by the
-   origin--is important for evaluating cached responses, origin servers
-   MUST include a Date header field in all responses. Clients SHOULD
-   only send a Date header field in messages that include an entity-
-   body, as in the case of the PUT and POST requests, and even then it
-   is optional. A received message which does not have a Date header
-   field SHOULD be assigned one by the recipient if the message will be
-   cached by that recipient or gatewayed via a protocol which requires a
-   Date.
-
-   In theory, the date SHOULD represent the moment just before the
-   entity is generated. In practice, the date can be generated at any
-   time during the message origination without affecting its semantic
-   value.

-   The format of the Date is an absolute date and time as defined by
-   HTTP-date in section 3.3; it MUST be sent in RFC1123 [8]-date format.

+   Origin servers MUST include a Date header field in all responses,
+   except in these cases:
 
+      1. If the response status code is 100 (Continue) or 101 (Switching
+         Protocols), the response MAY include a Date header field, at
+         the server's option.
+
+      2. If the response status code conveys a server error, e.g. 500
+         (Internal Server Error) or 503 (Service Unavailable), and it is
+         inconvenient or impossible to generate a valid Date.
+
+      3. If the server does not have a clock that can provide a
+         reasonable approximation of the current time, its responses
+         MUST NOT include a Date header field. In this case, the rules
+         in section 14.18.1 MUST be followed.
+
+   A received message that does not have a Date header field MUST be
+   assigned one by the recipient if the message will be cached by that
+   recipient or gatewayed via a protocol which requires a Date. An HTTP
+   implementation without a clock MUST NOT cache responses without
+   revalidating them on every use. An HTTP cache, especially a shared
+   cache, SHOULD use a mechanism, such as NTP [28], to synchronize its
+   clock with a reliable external standard.
+
+   Clients SHOULD only send a Date header field in messages that include
+   an entity-body, as in the case of the PUT and POST requests, and even
+   then it is optional. A client without a clock MUST NOT send a Date
+   header field in a request.
+
+   The HTTP-date sent in a Date header SHOULD NOT represent a date and
+   time subsequent to the generation of the message. It SHOULD represent
+   the best available approximation of the date and time of message
+   generation, unless the implementation has no means of generating a
+   reasonably accurate date and time. In theory, the date ought to
+   represent the moment just before the entity is generated. In
+   practice, the date can be generated at any time during the message
+   origination without affecting its semantic value.
+
+14.18.1 Clockless Origin Server Operation
+
+   Some origin server implementations might not have a clock available.
+   An origin server without a clock MUST NOT assign Expires or 
+   Last-Modified values to a response, unless these values were associated
+   with the resource by a system or user with a reliable clock. It MAY
+   assign an Expires value that is known, at or before server
+   configuration time, to be in the past (this allows "pre-expiration"
+   of responses without storing separate Expires values for each
+   resource).
+
+14.19 ETag
-14.20 ETag
 
-   The ETag entity-header field defines the entity tag for the
+   The ETag response-header field provides the current value of the
-   associated entity. The headers used with entity
+   entity tag for the requested variant. The headers used with entity
-   tags are described in sections 14.20, 14.25, 14.26 and 14.43. The entity tag
+   tags are described in sections 14.24, 14.26 and 14.44. The entity tag
-   may be used for comparison with other entities from the same resource
+   MAY be used for comparison with other entities from the same resource
-   (see section 13.3.2).
+   (see section 13.3.3).
 
 ETag = "ETag" ":" entity-tag
 
Examples:

ETag: "xyzzy"
ETag: W/"xyzzy"
ETag: ""
+
+14.20 Expect
+
+   The Expect request-header field is used to indicate that particular
+   server behaviors are required by the client.
+
+      Expect       =  "Expect" ":" 1#expectation
+
+      expectation  =  "100-continue" | expectation-extension
+      expectation-extension =  token [ "=" ( token | quoted-string )
+                               *expect-params ]
+      expect-params =  ";" token [ "=" ( token | quoted-string ) ]
+
+   A server that does not understand or is unable to comply with any of
+   the expectation values in the Expect field of a request MUST respond
+   with appropriate error status. The server MUST respond with a 417
+   (Expectation Failed) status if any of the expectations cannot be met
+   or, if there are other problems with the request, some other 4xx
+   status.
+
+   This header field is defined with extensible syntax to allow for
+   future extensions. If a server receives a request containing an
+   Expect field that includes an expectation-extension that it does not
+   support, it MUST respond with a 417 (Expectation Failed) status.
+
+   Comparison of expectation values is case-insensitive for unquoted
+   tokens (including the 100-continue token), and is case-sensitive for
+   quoted-string expectation-extensions.
+
+   The Expect mechanism is hop-by-hop: that is, an HTTP/1.1 proxy MUST
+   return a 417 (Expectation Failed) status if it receives a request
+   with an expectation that it cannot meet. However, the Expect
+   request-header itself is end-to-end; it MUST be forwarded if the
+   request is forwarded.
 
+   Many older HTTP/1.0 and HTTP/1.1 applications do not understand the
+   Expect header.
 
+   See section 8.2.3 for the use of the 100 (continue) status.
 
 14.21 Expires
 
    The Expires entity-header field gives the date/time after which the response
-   should be
+   is 
considered stale. A stale cache entry may not normally be returned by a cache (either a proxy cache or 
-  an 
+  a
user agent cache) unless it is first validated with the origin server (or with an
intermediate cache that has a fresh copy of the entity). See section
13.2 for further discussion of the expiration model.
 
    The presence of an Expires field does not imply that the original
    resource will change or cease to exist at, before, or after that
    time.
 
    The format is an absolute date and time as defined by HTTP-date in
-   section 3.3; it MUST be in RFC1123-date format:
+   section 3.3.1; it MUST be in RFC 1123 date format:
-
Expires = "Expires" ":" HTTP-date
 
    An example of its use is
 
Expires: Thu, 01 Dec 1994 16:00:00 GMT
 
Note: if a response includes a Cache-Control field with the max-age
-     directive,
+       directive (see section 14.9.3), 
that directive overrides the Expires field.
 
    HTTP/1.1 clients and caches MUST treat other invalid date formats,
    especially including the value "0", as in the past (i.e., "already
    expired").
 
-   To mark a response as "already expired," an origin server should use
+   To mark a response as "already expired," an origin server sends
an Expires date that is equal to the Date header value. (See the rules
for expiration calculations in section 13.2.4.)
 
-   To mark a response as "never expires," an origin server should use an
+   To mark a response as "never expires," an origin server sends an
    Expires date approximately one year from the time the response is
-   sent.  HTTP/1.1 servers should not send Expires dates more than one
+   sent. HTTP/1.1 servers SHOULD NOT send Expires dates more than one
    year in the future.
 
    The presence of an Expires header field with a date value of some
-   time in the future on an response that otherwise would by default be
+   time in the future on a response that otherwise would by default be
-   non-cacheable indicates that the response is cachable, unless
+   non-cacheable indicates that the response is cacheable, unless
    indicated otherwise by a Cache-Control header field (section 14.9).
 
 14.22 From
 
    The From request-header field, if given, SHOULD contain an Internet
    e-mail address for the human user who controls the requesting user
-   agent.  The address SHOULD be machine-usable, as defined by mailbox
+   agent. The address SHOULD be machine-usable, as defined by "mailbox"
-   in RFC 822 (as updated by RFC 1123 ):
+   in RFC 822 [9] as updated by RFC 1123 [8]:
 
From   = "From" ":" mailbox
 
    An example is:
 
From: webmaster@w3.org
 
    This header field MAY be used for logging purposes and as a means for
    identifying the source of invalid or unwanted requests. It SHOULD NOT
@@ -5544,121 +6059,71 @@
    is passed through a proxy the original issuer's address SHOULD be
    used.
 
-     Note: The client SHOULD not send the From header field without the
+   The client SHOULD NOT send the From header field without the
-     user's approval, as it may conflict with the user's privacy
+   user's approval, as it might conflict with the user's privacy
interests or their site's security policy. It is strongly
recommended that the user be able to disable, enable, and modify
the value of this field at any time prior to a request.
 
 14.23 Host
 
    The Host request-header field specifies the Internet host and port
    number of the resource being requested, as obtained from the original
-   URL given by the user or referring resource (generally an HTTP URL,
+   URI given by the user or referring resource (generally an HTTP URL,
    as described in section 3.2.2). The Host field value MUST represent
-   the network location of the origin server or gateway given by the
+   the naming authority of the origin server or gateway given by the
    original URL. This allows the origin server or gateway to
    differentiate between internally-ambiguous URLs, such as the root "/"
    URL of a server for multiple host names on a single IP address.
 
Host = "Host" ":" host [ ":" port ] ; Section 3.2.2
 
    A "host" without any trailing port information implies the default
    port for the service requested (e.g., "80" for an HTTP URL). For
    example, a request on the origin server for
-   <http://www.w3.org/pub/WWW/> MUST include:
+   <http://www.w3.org/pub/WWW/> would properly include:
 
GET /pub/WWW/ HTTP/1.1
Host: www.w3.org
 
    A client MUST include a Host header field in all HTTP/1.1 request
-   messages on the Internet (i.e., on any message corresponding to a
+   messages . If the
-   request for a URL which includes an Internet host address for the
+   requested URI does not include an Internet host name for the
-   service being requested). If the Host field is not already present,
+ service being requested, then the Host header field MUST be given with an empty value.
-   an HTTP/1.1 proxy MUST add a Host field to the request message prior
+   An HTTP/1.1 proxy MUST ensure that any request message 
-   to forwarding it on the Internet.
+  it forwards does contain an appropriate Host header
+   field that identifies the service being requested by the proxy.
All Internet-based HTTP/1.1 servers MUST respond with a 400
+   (Bad Request)
status code to any HTTP/1.1 request message
which lacks a Host header field.
-
-   See sections 5.2 and 19.5.1 for other requirements relating to Host.
+   See sections 5.2 and 19.6.1.1 for other requirements relating to Host.
-
-14.24 If-Modified-Since
+14.25 If-Modified-Since
-
-   The If-Modified-Since request-header field is used with the GET method to
+   The If-Modified-Since request-header field is used with a method to
make it conditional: if the requested variant has not been modified
since the time specified in this field, an entity will not be
returned from the server; instead, a 304 (not modified) response will
be returned without any message-body.
-
If-Modified-Since = "If-Modified-Since" ":" HTTP-date
-
An example of the field is:
-
If-Modified-Since: Sat, 29 Oct 1994 19:43:31 GMT
-
A GET method with an If-Modified-Since header and no Range header
requests that the identified entity be transferred only if it has
been modified since the date given by the If-Modified-Since header.
The algorithm for determining this includes the following cases:
-
a) If the request would normally result in anything other than a
200 (OK) status, or if the passed If-Modified-Since date is
invalid, the response is exactly the same as for a normal GET.
A date which is later than the server's current time is invalid.
+        
-
b) If the variant has been modified since the If-Modified-Since date,
the response is exactly the same as for a normal GET.
-
c) If the variant has not been modified since a valid If-Modified-Since date, the server 
-     MUST
+     SHOULD 
return a 304 (Not Modified) response.
-
The purpose of this feature is to allow efficient updates of cached
information with a minimum amount of transaction overhead.
-
-     Note that the Range request-header field modifies the meaning of
+      Note: The Range request-header field modifies the meaning of 
-     If-Modified-Since; see section 14.36 for full details.
+      If-Modified-Since; see section 14.35 for full details.
-
-     Note that If-Modified-Since times are interpreted by the server,
+      Note: If-Modified-Since times are interpreted by the server,
-     whose clock may not be synchronized with the client.
+      whose clock might not be synchronized with the client.
 
+      Note: When handling an If-Modified-Since header field, some
+      servers will use an exact date comparison function, rather than a
+      less-than function, for deciding whether to send a 304 (Not
+      Modified) response. To get best results when sending an If-
+      Modified-Since header field for cache validation, clients are
+      advised to use the exact date string received in a previous Last-
+      Modified header field whenever possible.
+
-   Note that if a client uses an arbitrary date in the If-Modified-Since
+   Note: If a client uses an arbitrary date in the If-Modified-Since
header instead of a date taken from the Last-Modified header for
the same request, the client should be aware of the fact that this
date is interpreted in the server's understanding of time. The
client should consider unsynchronized clocks and rounding problems
due to the different encodings of time between the client and
server. This includes the possibility of race conditions if the
document has changed between the time it was first requested and
the If-Modified-Since date of a subsequent request, and the
possibility of clock-skew-related problems if the If-Modified-Since
date is derived from the client's clock without correction
to the server's clock. Corrections for different time bases
between client and server are at best approximate due to network latency.

+   The result of a request having both an If-Modified-Since header field
+   and either an If-Match or an If-Unmodified-Since header fields is
+   undefined by this specification.

-14.25 If-Match
+14.24 If-Match
 
    The If-Match request-header field is used with a method to make it
    conditional. A client that has one or more entities previously
    obtained from the resource can verify that one of those entities is
    current by including a list of their associated entity tags in the If-Match header field.
+   Entity tags are defined in section 3.11.
The purpose of this feature is to allow efficient updates of cached
-   information with a minimum amount of transaction overhead.
+   information with a minimum amount of transaction overhead.
It is also used, on updating requests, to prevent inadvertent modification of
the wrong version of a resource. As a special case, the value "*"
matches any current entity of the resource.
 
If-Match = "If-Match" ":" ( "*" | 1#entity-tag )
 
    If any of the entity tags match the entity tag of the entity that
    would have been returned in the response to a similar GET request
    (without the If-Match header) on that resource, or if "*" is given
    and any current entity exists for that resource, then the server MAY
    perform the requested method as if the If-Match header field did not
    exist.
 
-   A server MUST use the strong comparison function (see section 3.11)
+   A server MUST use the strong comparison function (see section 13.3.3)
    to compare the entity tags in If-Match.
 
    If none of the entity tags match, or if "*" is given and no current
@@ -5669,26 +6134,98 @@
    last retrieved it.
 
    If the request would, without the If-Match header field, result in
-   anything other than a 2xx status, then the If-Match header
+   anything other than a 2xx or 412 status, then the If-Match header
MUST be ignored.
 
    The meaning of "If-Match: *" is that the method SHOULD be performed
    if the representation selected by the origin server (or by a cache,
-   possibly using the Vary mechanism, see section 14.43) exists, and
+   possibly using the Vary mechanism, see section 14.44) exists, and
    MUST NOT be performed if the representation does not exist.
 
-
    A request intended to update a resource (e.g., a PUT) MAY include an
    If-Match header field to signal that the request method MUST NOT be
    applied if the entity corresponding to the If-Match value (a single
entity tag) is no longer a representation of that resource. This
    allows the user to indicate that they do not wish the request to be
    successful if the resource has been changed without their knowledge.
    Examples:
 
If-Match: "xyzzy"
If-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-Match: *
+
+   The result of a request having both an If-Match header field and
+   either an If-None-Match or an If-Modified-Since header fields is
+   undefined by this specification.
 
 14.26 If-None-Match
 
@@ -5698,52 +6235,62 @@
    current by including a list of their associated entity tags in the
    If-None-Match header field. The purpose of this feature is to allow
    efficient updates of cached information with a minimum amount of
-   transaction overhead. It is also used, on updating requests, to prevent
+   transaction overhead. It is also used to prevent a method (e.g. PUT)
-   inadvertent modification of a resource which
+   from inadvertently modifying an existing resource when the client
-   was not known to exist.
+   believes that the resource does not exist.
 
    As a special case, the value "*" matches any current entity of the
    resource.
 
If-None-Match = "If-None-Match" ":" ( "*" | 1#entity-tag )
 
    If any of the entity tags match the entity tag of the entity that
    would have been returned in the response to a similar GET request
    (without the If-None-Match header) on that resource, or if "*" is
    given and any current entity exists for that resource, then the
-   server MUST NOT perform the requested method. Instead, if the request
+   server MUST NOT perform the requested method, unless required to do
+   so because the resource's modification date fails to match that
+   supplied in an If-Modified-Since header field in the request.
-   method was GET or HEAD, the server SHOULD
+   Instead, if the request method was GET or HEAD, the server SHOULD
respond with a 304 (Not Modified) response, including the cache-related
-    entity-header fields
+    header fields
(particularly ETag) of one of the entities that matched. For all
other request methods, the server MUST respond with a status of
412 (Precondition Failed).
 
-   See section 13.3.3 for rules on how to determine if two entity tags
+   See section 13.3.3 for rules on how to determine if two entities tags
    match. The weak comparison function can only be used with GET or HEAD
    requests.
 
-   If none of the entity tags match, or if "*" is given and no current
+   If none of the entity tags match,
-   entity exists, then the server MAY perform the requested method as if
+   then the server MAY perform the requested method as if
the If-None-Match header field did not exist
-   .
+   , but MUST also ignore any If-Modified-Since header field(s) in the
+   request. That is, if no entity tags match, then the server MUST NOT
+   return a 304 (Not Modified) response.
 
    If the request would, without the If-None-Match header field, result
-   in anything other than a 2xx status, then the If-None-Match
+   in anything other than a 2xx or 304 status, then the If-None-Match
header MUST be ignored.
+   (See section 13.3.4 for a discussion of
+   server behavior when both If-Modified-Since and If-None-Match appear
+   in the same request.)
 
    The meaning of "If-None-Match: *" is that the method MUST NOT be
    performed if the representation selected by the origin server (or by
-   a cache, possibly using the Vary mechanism, see section 14.43)
+   a cache, possibly using the Vary mechanism, see section 14.44)
    exists, and SHOULD be performed if the representation does not exist.
-   This feature may be useful in preventing races between PUT
+   This feature is intended to be useful in preventing races between PUT
    operations.
 
    Examples:
 
If-None-Match: "xyzzy"
If-None-Match: W/"xyzzy"
If-None-Match: "xyzzy", "r2d2xxxx", "c3piozzzz"
If-None-Match: W/"xyzzy", W/"r2d2xxxx", W/"c3piozzzz"
If-None-Match: *
+
+   The result of a request having both an If-None-Match header field and
+   either an If-Match or an If-Unmodified-Since header fields is
+   undefined by this specification.
 
 14.27 If-Range
 
@@ -5758,30 +6305,29 @@
    The If-Range header allows a client to "short-circuit" the second
    request. Informally, its meaning is `if the entity is unchanged, send
    me the part(s) that I am missing; otherwise, send me the entire new
-   entity.'
+   entity'.
 
If-Range = "If-Range" ":" ( entity-tag | HTTP-date )
 
    If the client has no entity tag for an entity, but does have a Last-
-   Modified date, it may use that date in a If-Range header. (The
+   Modified date, it MAY use that date in an If-Range header. (The
server can distinguish between a valid HTTP-date and any form of
entity-tag by examining no more than two characters.) The If-Range
-   header should only be used together with a Range header, and must be
+   header SHOULD only be used together with a Range header, and MUST be
ignored if the request does not include a Range header, or if the
server does not support the sub-range operation.
 
    If the entity tag given in the If-Range header matches the current
-   entity tag for the entity, then the server should provide the
+   entity tag for the entity, then the server SHOULD provide the
    specified sub-range of the entity using a 206 (Partial content)
-   response. If the entity tag does not match, then the server should
+   response. If the entity tag does not match, then the server SHOULD
    return the entire entity using a 200 (OK) response.
 
 14.28 If-Unmodified-Since
 
    The If-Unmodified-Since request-header field is used with a method to
    make it conditional. If the requested resource has not been modified
-   since the time specified in this field, the server should perform the
+   since the time specified in this field, the server SHOULD perform the
    requested operation as if the If-Unmodified-Since header were not
    present.
 
@@ -5789,28 +6335,32 @@
    the server MUST NOT perform the requested operation, and MUST return
    a 412 (Precondition Failed).
 
If-Unmodified-Since = "If-Unmodified-Since" ":" HTTP-date
 
    An example of the field is:
 
If-Unmodified-Since: Sat, 29 Oct 1994 19:43:31 GMT
 
    If the request normally (i.e., without the If-Unmodified-Since
-   header) would result in anything other than a 2xx status, the 
+   header) would result in anything other than a 2xx or 412 status, the
-   If-Unmodified-Since header should be ignored.
+   If-Unmodified-Since header SHOULD be ignored.
 
    If the specified date is invalid, the header is ignored.
 
+   The result of a request having both an If-Unmodified-Since header
+   field and either an If-None-Match or an If-Modified-Since header
+   fields is undefined by this specification.
+
 14.29 Last-Modified
 
    The Last-Modified entity-header field indicates the date and time at
    which the origin server believes the variant was last modified.
 
Last-Modified  = "Last-Modified" ":" HTTP-date
 
    An example of its use is
 
Last-Modified: Tue, 15 Nov 1994 12:45:26 GMT
 
    The exact meaning of this header field depends on the implementation
    of the origin server and the nature of the original resource. For
@@ -5826,7 +6376,7 @@
    future, the server MUST replace that date with the message
    origination date.
 
-   An origin server should obtain the Last-Modified value of the entity
+   An origin server SHOULD obtain the Last-Modified value of the entity
    as close as possible to the time that it generates the Date value of
    its response. This allows a recipient to make an accurate assessment
    of the entity's modification time, especially if the entity changes
@@ -5840,82 +6390,83 @@
    to a location other than the Request-URI for completion of the
    request or identification of a new resource. For 201 (Created)
    responses, the Location is that of the new resource which was created
by the request. For 3xx responses, the location SHOULD indicate the
-   server's preferred URL for automatic redirection to the resource. The
+   server's preferred URI for automatic redirection to the resource. The
-   field value consists of a single absolute URL.
+   field value consists of a single absolute URI.
 
Location       = "Location" ":" absoluteURI [INS[[INS[{errata}]] [ "#" fragment ] ]]
 
-   An example is
+   An example is:
 
Location: http://www.w3.org/pub/WWW/People.html
 
-     Note: The Content-Location header field (section 14.15) differs
+     Note: The Content-Location header field (section 14.14) differs
from Location in that the Content-Location identifies the original
location of the entity enclosed in the request. It is therefore
possible for a response to contain header fields for both Location
and Content-Location. Also see section 13.10 for cache requirements of some methods.
 
 14.31 Max-Forwards
 
-   The Max-Forwards request-header field may be used with the
+   The Max-Forwards request-header field provides a mechanism with the
-   TRACE method (section 14.31) to limit the
+   TRACE (section 9.8) and OPTIONS (section 9.2) methods to limit the
number of proxies or gateways that can forward the request to the
next inbound server. This can be useful when the client is attempting
to trace a request chain which appears to be failing or looping in mid-chain.
 
Max-Forwards   = "Max-Forwards" ":" 1*DIGIT
 
    The Max-Forwards value is a decimal integer indicating the remaining
    number of times this request message may be forwarded.
 
-   Each proxy or gateway recipient of a TRACE request
+   Each proxy or gateway recipient of a TRACE or OPTIONS request
-   containing a  Max-Forwards header field SHOULD check and update
+   containing a Max-Forwards header field MUST check and update
its value prior to forwarding the request. If the received value is zero
-   (0), the recipient SHOULD NOT forward the request; instead, it SHOULD
+   (0), the recipient MUST NOT forward the request; instead, it MUST
-   respond as the final recipient with a 200 (OK) response containing the
+   respond as the final recipient.
-   received request message as the response entity-body (as described in section 9.8).
If the received Max-Forwards value is greater than zero, then the forwarded message
-   SHOULD
+   MUST
contain an updated Max-Forwards field with a value decremented by one (1).
 
-   The Max-Forwards header field SHOULD be ignored for all other methods
+   The Max-Forwards header field MAY be ignored for all other methods
    defined by this specification and for any extension methods for which
    it is not explicitly referred to as part of that method definition.
 
 14.32 Pragma
 
    The Pragma general-header field is used to include implementation-
-   specific directives that may apply to any recipient along the
+   specific directives that might apply to any recipient along the
    request/response chain. All pragma directives specify optional
    behavior from the viewpoint of the protocol; however, some systems
    MAY require that behavior be consistent with the directives.
 
 Pragma            = "Pragma" ":" 1#pragma-directive

  pragma-directive  = "no-cache" | extension-pragma
  extension-pragma  = token [ "=" ( token | quoted-string ) ]
 
    When the no-cache directive is present in a request message, an
    application SHOULD forward the request toward the origin server even
    if it has a cached copy of what is being requested. This pragma
    directive has the same semantics as the no-cache cache-directive (see
-   section 14.9) and is defined here for backwards compatibility with
+   section 14.9) and is defined here for backward compatibility with
HTTP/1.0. Clients SHOULD include both header fields when a no-cache
    request is sent to a server not known to be HTTP/1.1 compliant.
 
    Pragma directives MUST be passed through by a proxy or gateway
    application, regardless of their significance to that application,
-   since the directives may be applicable to all recipients along the
+   since the directives might be applicable to all recipients along the
    request/response chain. It is not possible to specify a pragma for a
    specific recipient; however, any pragma directive not relevant to a
    recipient SHOULD be ignored by that recipient.
 
-   HTTP/1.1 clients SHOULD NOT send the Pragma request-header.
HTTP/1.1 caches SHOULD treat "Pragma: no-cache" as if the client had
sent "Cache-Control: no-cache". No new Pragma directives will be defined in HTTP.

+      Note: because the meaning of "Pragma: no-cache as a response
+      header field is not actually specified, it does not provide a
+      reliable replacement for "Cache-Control: no-cache" in a response
 
 14.33 Proxy-Authenticate
 
@@ -5924,83 +6475,59 @@
    consists of a challenge that indicates the authentication scheme and
    parameters applicable to the proxy for this Request-URI.
 
-          Proxy-Authenticate  = "Proxy-Authenticate" ":" challenge
+       Proxy-Authenticate  = "Proxy-Authenticate" ":" 1#challenge
 
The HTTP access authentication process is described in
-   section 11.
+   "HTTP Authentication: Basic and Digest Access Authentication" [43].
Unlike WWW-Authenticate, the Proxy-Authenticate header field applies
only to the current connection and SHOULD NOT be passed on to downstream clients.
-   However, an intermediate proxy may need to obtain
+   However, an intermediate proxy might need to obtain
its own credentials by requesting them from the downstream client,
which in some circumstances will appear as if the proxy is forwarding
the Proxy-Authenticate header field.
 
 14.34 Proxy-Authorization
 
    The Proxy-Authorization request-header field allows the client to
    identify itself (or its user) to a proxy which requires
authentication. The Proxy-Authorization field value consists of
    credentials containing the authentication information of the user
    agent for the proxy and/or realm of the resource being requested.
 
        Proxy-Authorization     = "Proxy-Authorization" ":" credentials
 
The HTTP access authentication process is described in
-   section 11.
+   "HTTP Authentication: Basic and Digest Access Authentication" [43] .
Unlike Authorization, the Proxy-Authorization header field applies
only to the next outbound proxy that demanded authentication using
the Proxy-Authenticate field. When multiple proxies are used in a chain,
the  Proxy-Authorization header field is consumed by the first outbound
proxy that was expecting to receive credentials. A proxy MAY relay
the credentials from the client request to the next proxy if that is
the mechanism by which the proxies cooperatively authenticate a given request.
-
-14.35 Public
-
-   The Public response-header field lists the set of methods supported
-   by the server. The purpose of this field is strictly to inform the
-   recipient of the capabilities of the server regarding unusual
-   methods.  The methods listed may or may not be applicable to the
-
-   Request-URI; the Allow header field (section 14.7) MAY be used to
-   indicate methods allowed for a particular URI.
-
-          Public         = "Public" ":" 1#method
-
-   Example of use:
-
-          Public: OPTIONS, MGET, MHEAD, GET, HEAD
-
-   This header field applies only to the server directly connected to
-   the client (i.e., the nearest neighbor in a chain of connections). If
-   the response passes through a proxy, the proxy MUST either remove the
-   Public header field or replace it with one applicable to its own
-   capabilities.
 
-14.36 Range
+14.35 Range
 
-14.36.1 Byte Ranges
+14.35.1 Byte Ranges
 
    Since all HTTP entities are represented in HTTP messages as sequences
    of bytes, the concept of a byte range is meaningful for any HTTP
entity. (However, not all clients and servers need to support byte-range operations.)
 
    Byte range specifications in HTTP apply to the sequence of bytes in
    the entity-body (not necessarily the same as the message-body).
 
-   A byte range operation may specify a single range of bytes, or a set
+   A byte range operation MAY specify a single range of bytes, or a set
    of ranges within a single entity.
 
        ranges-specifier = byte-ranges-specifier
        byte-ranges-specifier = bytes-unit "=" byte-range-set
        byte-range-set  = 1#( byte-range-spec | suffix-byte-range-spec )
        byte-range-spec = first-byte-pos "-" [last-byte-pos]
        first-byte-pos  = 1*DIGIT
        last-byte-pos   = 1*DIGIT
 
    The first-byte-pos value in a byte-range-spec gives the byte-offset
@@ -6008,10 +6535,12 @@
    byte-offset of the last byte in the range; that is, the byte
    positions specified are inclusive. Byte offsets start at zero.
 
-   If the last-byte-pos value is present, it must be greater than or
+   If the last-byte-pos value is present, it MUST be greater than or
    equal to the first-byte-pos in that byte-range-spec, or the byte-
-   range-spec is invalid. The recipient of
+   range-spec is syntactically invalid. The recipient of
-   an invalid byte-range-spec must ignore it.
+    a byte-range-set that includes one or more syntactically invalid byte-range-spec
+   values MUST ignore the header field that includes that byte-range-set.
 
    If the last-byte-pos value is absent, or if the value is greater than
    or equal to the current length of the entity-body, last-byte-pos is
@@ -6021,9 +6550,8 @@
    By its choice of last-byte-pos, a client can limit the number of
    bytes retrieved without knowing the size of the entity.
 
suffix-byte-range-spec = "-" suffix-length
suffix-length = 1*DIGIT
 
    A suffix-byte-range-spec is used to specify the suffix of the
    entity-body, of a length given by the suffix-length value. (That is,
@@ -6031,47 +6559,48 @@
    entity is shorter than the specified suffix-length, the entire
    entity-body is used.
 
+   If a syntactically valid byte-range-set includes at least one byte-
+   range-spec whose first-byte-pos is less than the current length of
+   the entity-body, or at least one suffix-byte-range-spec with a non-
+   zero suffix-length, then the byte-range-set is satisfiable.
+   Otherwise, the byte-range-set is unsatisfiable. If the byte-range-set
+   is unsatisfiable, the server SHOULD return a response with a status
+   of 416 (Requested range not satisfiable). Otherwise, the server
+   SHOULD return a response with a status of 206 (Partial Content)
+   containing the satisfiable ranges of the entity-body.
+
    Examples of byte-ranges-specifier values (assuming an entity-body of
    length 10000):
 
-     o  The first 500 bytes (byte offsets 0-499, inclusive):
-          bytes=0-499
+      - The first 500 bytes (byte offsets 0-499, inclusive):  bytes=0-
+        499
-
-
-     o  The second 500 bytes (byte offsets 500-999, inclusive):
+      - The second 500 bytes (byte offsets 500-999, inclusive):
bytes=500-999
-
 
-     o  The final 500 bytes (byte offsets 9500-9999, inclusive):
+      - The final 500 bytes (byte offsets 9500-9999, inclusive):
bytes=-500
 
-     o  Or
+      - Or bytes=9500-
-          bytes=9500-
 
-     o  The first and last bytes only (bytes 0 and 9999):
+      - The first and last bytes only (bytes 0 and 9999):  bytes=0-0,-1
-          bytes=0-0,-1
 
+      - Several legal but not canonical specifications of the second 500
+        bytes (byte offsets 500-999, inclusive):
-     o  Several legal but not canonical specifications of the second
-        500 bytes (byte offsets 500-999, inclusive):
 bytes=500-600,601-999
 bytes=500-700,601-999
 
-14.36.2 Range Retrieval Requests
+14.35.2 Range Retrieval Requests
 
    HTTP retrieval requests using conditional or unconditional GET
-   methods may request one or more sub-ranges of the entity, instead of
+   methods MAY request one or more sub-ranges of the entity, instead of
    the entire entity, using the Range request header, which applies to
    the entity returned as the result of the request:
 
Range = "Range" ":" ranges-specifier
 
    A server MAY ignore the Range header. However, HTTP/1.1 origin
-   servers and intermediate caches SHOULD support byte ranges when
+   servers and intermediate caches ought to support byte ranges when
    possible, since Range supports efficient recovery from partially
    failed transfers, and supports efficient partial retrieval of large
    entities.
@@ -6079,28 +6608,28 @@
    If the server supports the Range header and the specified range or
    ranges are appropriate for the entity:
 
-     o  The presence of a Range header in an unconditional GET modifies
+      - The presence of a Range header in an unconditional GET modifies
         what is returned if the GET is otherwise successful. In other
         words, the response carries a status code of 206 (Partial
         Content) instead of 200 (OK).
 
-     o  The presence of a Range header in a conditional GET (a request
+      - The presence of a Range header in a conditional GET (a request
         using one or both of If-Modified-Since and If-None-Match, or
         one or both of If-Unmodified-Since and If-Match) modifies what
is returned if the GET is otherwise successful and the condition
is true. It does not affect the 304 (Not Modified) response
returned if the conditional is false.
 
-   In some cases, it may be more appropriate to use the If-Range
+   In some cases, it might be more appropriate to use the If-Range
header (see section 14.27) in addition to the Range header.
 
    If a proxy that supports ranges receives a Range request, forwards
    the request to an inbound server, and receives an entire entity in
    reply, it SHOULD only return the requested range to its client. It
-   SHOULD store the entire received response in its cache, if that is
+   SHOULD store the entire received response in its cache if that is
    consistent with its cache allocation policies.
 
-14.37 Referer
+14.36 Referer
 
    The Referer[sic] request-header field allows the client to specify,
    for the server's benefit, the address (URI) of the resource from
@@ -6112,41 +6641,36 @@
    sent if the Request-URI was obtained from a source that does not have
    its own URI, such as input from the user keyboard.
 
Referer        = "Referer" ":" ( absoluteURI | relativeURI )
 
    Example:
 
Referer: http://www.w3.org/hypertext/DataSources/Overview.html
-
-   If the field value is a partial URI, it SHOULD be interpreted
+   If the field value is a relative URI, it SHOULD be interpreted
relative to the Request-URI. The URI MUST NOT include a fragment.
+   See section 15.1.3 for security considerations.
 
-     Note: Because the source of a link may be private information or
-     may reveal an otherwise private information source, it is strongly
-     recommended that the user be able to select whether or not the
-     Referer field is sent. For example, a browser client could have a
-     toggle switch for browsing openly/anonymously, which would
-     respectively enable/disable the sending of Referer and From
-     information.
 
-14.38 Retry-After
+14.37 Retry-After
 
    The Retry-After response-header field can be used with a 503 (Service
    Unavailable) response to indicate how long the service is expected to
be unavailable to the requesting client.
+   This field MAY also be used with any 3xx (Redirection) response to indicate the minimum time the
+   user-agent is asked wait before issuing the redirected request.
The value of this field can be either an HTTP-date or an integer number of
seconds (in decimal) after the time of the response.
 
Retry-After  = "Retry-After" ":" ( HTTP-date | delta-seconds )
 
    Two examples of its use are
 
Retry-After: Fri, 31 Dec 1999 23:59:59 GMT
Retry-After: 120
 
    In the latter example, the delay is 2 minutes.
 
-14.39 Server
+14.38 Server
 
    The Server response-header field contains information about the
    software used by the origin server to handle the request. The field
@@ -6155,54 +6679,141 @@
    tokens are listed in order of their significance for identifying the
    application.
 
Server         = "Server" ":" 1*( product | comment )
 
    Example:
 
Server: CERN/3.0 libwww/2.17
 
    If the response is being forwarded through a proxy, the proxy
    application MUST NOT modify the Server response-header. Instead, it
-   SHOULD include a Via field (as described in section 14.44).
+   [DEL[[INS[{2616}]] SHOULD]] [INS[[INS[{errata}]] MUST]] include a Via field (as described in section 14.45).
+
-     Note: Revealing the specific software version of the server may
+     Note: Revealing the specific software version of the server might
allow the server machine to become more vulnerable to attacks
against software that is known to contain security holes. Server
implementors are encouraged to make this field a configurable option.
+
+14.39 TE
+
+   The TE request-header field indicates what extension transfer-codings
+   it is willing to accept in the response and whether or not it is
+   willing to accept trailer fields in a chunked transfer-coding. Its
+   value may consist of the keyword "trailers" and/or a comma-separated
+   list of extension transfer-coding names with optional accept
+   parameters (as described in section 3.6).
+
+       TE        = "TE" ":" #( t-codings )
+       t-codings = "trailers" | ( transfer-extension [ accept-params ] )
+
+   The presence of the keyword "trailers" indicates that the client is
+   willing to accept trailer fields in a chunked transfer-coding, as
+   defined in section 3.6.1. This keyword is reserved for use with
+   transfer-coding values even though it does not itself represent a
+   transfer-coding.
+
+   Examples of its use are:
+
+       TE: deflate
+       TE:
+       TE: trailers, deflate;q=0.5
+
+   The TE header field only applies to the immediate connection.
+   Therefore, the keyword MUST be supplied within a Connection header
+   field (section 14.10) whenever TE is present in an HTTP/1.1 message.
+
+   A server tests whether a transfer-coding is acceptable, according to
+   a TE field, using these rules:
+
+      1. The "chunked" transfer-coding is always acceptable. If the
+         keyword "trailers" is listed, the client indicates that it is
+         willing to accept trailer fields in the chunked response on
+         behalf of itself and any downstream clients. The implication is
+         that, if given, the client is stating that either all
+         downstream clients are willing to accept trailer fields in the
+         forwarded response, or that it will attempt to buffer the
+         response on behalf of downstream recipients.
+
+         Note: HTTP/1.1 does not define any means to limit the size of a
+         chunked response such that a client can be assured of buffering
+         the entire response.
+
+      2. If the transfer-coding being tested is one of the transfer-
+         codings listed in the TE field, then it is acceptable unless it
+         is accompanied by a qvalue of 0. (As defined in section 3.9, a
+         qvalue of 0 means "not acceptable.")
+
+      3. If multiple transfer-codings are acceptable, then the
+         acceptable transfer-coding with the highest non-zero qvalue is
+         preferred.  The "chunked" transfer-coding always has a qvalue
+         of 1.
 
+   If the TE field-value is empty or if no TE field is present, the only
+   transfer-coding  is "chunked". A message with no transfer-coding is
+   always acceptable.
 
+14.40 Trailer
+
+   The Trailer general field value indicates that the given set of
+   header fields is present in the trailer of a message encoded with
+   chunked transfer-coding.
+
+       Trailer  = "Trailer" ":" 1#field-name
+
+   An HTTP/1.1 message SHOULD include a Trailer header field in a
+   message using chunked transfer-coding with a non-empty trailer. Doing
+   so allows the recipient to know which header fields to expect in the
+   trailer.
+
+   If no Trailer header field is present, the trailer SHOULD NOT include
+   any header fields. See section 3.6.1 for restrictions on the use of
+   trailer fields in a "chunked" transfer-coding.
+
+   Message header fields listed in the Trailer header field MUST NOT
+   include the following header fields:
+
+      . Transfer-Encoding
+
+      . Content-Length
+
+      . Trailer
+
-14.40 Transfer-Encoding
+14.41 Transfer-Encoding
 
    The Transfer-Encoding general-header field indicates what (if any)
    type of transformation has been applied to the message body in order
    to safely transfer it between the sender and the recipient. This
-   differs from the Content-Encoding in that the transfer coding is a
+   differs from the content-coding in that the transfer-coding is a
    property of the message, not of the entity.
 
Transfer-Encoding       = "Transfer-Encoding" ":" 1#transfer-coding
+
-   Transfer codings are defined in section 3.6. An example is:
+   Transfer-codings are defined in section 3.6. An example is:
 
Transfer-Encoding: chunked
 
+   If multiple encodings have been applied to an entity, the transfer-
+   codings MUST be listed in the order in which they were applied.
+   Additional information about the encoding parameters MAY be provided
+   by other entity-header fields not defined by this specification.
 
    Many older HTTP/1.0 applications do not understand the Transfer-Encoding header.
 
-14.41 Upgrade
+14.42 Upgrade
 
    The Upgrade general-header allows the client to specify what
    additional communication protocols it supports and would like to use
    if the server finds it appropriate to switch protocols. The server
    MUST use the Upgrade header field within a 101 (Switching Protocols)
    response to indicate which protocol(s) are being switched.
 
Upgrade        = "Upgrade" ":" 1#product
 
    For example,
 
Upgrade: HTTP/2.0, SHTTP/1.3, IRC/6.9, RTA/x11
 
    The Upgrade header field is intended to provide a simple mechanism
    for transition from HTTP/1.1 to some other, incompatible protocol. It
@@ -6241,7 +6852,7 @@
    will only be useful if both the client and server associate the name
    with the same protocol.
 
-14.42 User-Agent
+14.43 User-Agent
 
    The User-Agent request-header field contains information about the
    user agent originating the request. This is for statistical purposes,
@@ -6254,88 +6865,66 @@
    are listed in order of their significance for identifying the
    application.
 
User-Agent     = "User-Agent" ":" 1*( product | comment )
 
    Example:
 
User-Agent: CERN-LineMode/2.15 libwww/2.17b3
 
-14.43 Vary
+14.44 Vary
 
-   The Vary response-header field is used by a server to signal that the
-   response entity was selected from the available representations of
-   the response using server-driven negotiation (section 12). Field-
-   names listed in Vary headers are those of request-headers. The Vary
-   field value indicates either that the given set of header fields
-   encompass the dimensions over which the representation might vary, or
-   that the dimensions of variance are unspecified ("*") and thus may
-   vary over any aspect of future requests.
+   The Vary field value indicates the set of request-header fields that
+   fully determines, while the response is fresh, whether a cache is
+   permitted to use the response to reply to a subsequent request
+   without revalidation. For uncacheable or stale responses, the Vary
+   field value advises the user agent about the criteria that were used
+   to select the representation. A Vary field value of "*" implies that
+   a cache cannot determine from the request headers of a subsequent
+   request whether this response is the appropriate representation. See
+   section 13.6 for use of the Vary header field by caches.
 
Vary  = "Vary" ":" ( "*" | 1#field-name )
 
-   An HTTP/1.1 server MUST include an appropriate Vary header field with any
+   An HTTP/1.1 server SHOULD include a Vary header field with any
-   cachable response that is subject to server-driven negotiation.
+   cacheable response that is subject to server-driven negotiation.
    Doing so allows a cache to properly interpret future requests on that
    resource and informs the user agent about the presence of negotiation
-   on that resource. A server SHOULD include an appropriate Vary header
+   on that resource. A server MAY include a Vary header
-   field with a non-cachable response that is subject to server-driven negotiation, 
+   field with a non-cacheable response that is subject to server-driven negotiation,
since this might provide the user agent with useful information about
-   the dimensions over which the response might vary.
+   the dimensions over which the response varies at the time of the response.
-
-   The set of header fields named by the Vary field value is known as
-   the "selecting" request-headers.
-
-   When the cache receives a subsequent request whose Request-URI
-   specifies one or more cache entries including a Vary header, the
-   cache MUST NOT use such a cache entry to construct a response to the
-   new request unless all of the headers named in the cached Vary header
-
-   are present in the new request, and all of the stored selecting
-   request-headers from the previous request match the corresponding
-   headers in the new request.
 
-   The selecting request-headers from two requests are defined to match
-   if and only if the selecting request-headers in the first request can
-   be transformed to the selecting request-headers in the second request
-   by adding or removing linear whitespace (LWS) at places where this is
-   allowed by the corresponding BNF, and/or combining multiple message-
-   header fields with the same field name following the rules about
-   message headers in section 4.2.
-
-   A Vary field value of "*" signals that unspecified parameters,
-   possibly other than the contents of request-header fields (e.g., the
-   network address of the client), play a role in the selection of the
-   response representation. Subsequent requests on that resource can
-   only be properly interpreted by the origin server, and thus a cache
-   MUST forward a (possibly conditional) request even when it has a
-   fresh response cached for the resource. See section 13.6 for use of
-   the Vary header by caches.
 
    A Vary field value consisting of a list of field-names signals that
    the representation selected for the response is based on a selection
    algorithm which considers ONLY the listed request-header field values
    in selecting the most appropriate representation. A cache MAY assume
    that the same selection will be made for future requests with the
-   same values for the listed field names, for the duration of time in
+   same values for the listed field names, for the duration of time for
    which the response is fresh.
 
    The field-names given are not limited to the set of standard
    request-header fields defined by this specification. Field names are
    case-insensitive.
 
+   A Vary field value of "*" signals that unspecified parameters not
+   limited to the request-headers (e.g., the network address of the
+   client), play a role in the selection of the response representation.
+   The "*" value MUST NOT be generated by a proxy server; it may only be
+   generated by an origin server.
+
-14.44 Via
+14.45  Via
 
    The Via general-header field MUST be used by gateways and proxies to
    indicate the intermediate protocols and recipients between the user
    agent and the server on requests, and between the origin server and
    the client on responses. It is analogous to the "Received" field of
-   RFC 822 and is intended to be used for tracking message forwards,
+   RFC 822 [9] and is intended to be used for tracking message forwards,
    avoiding request loops, and identifying the protocol capabilities of
    all senders along the request/response chain.
 
-
       Via =  "Via" ":" 1#( received-protocol received-by [ comment ] )
-
       received-protocol = [ protocol-name "/" ] protocol-version
       protocol-name     = token
       protocol-version  = token
@@ -6356,7 +6945,7 @@
    it MAY be replaced by a pseudonym. If the port is not given, it MAY
    be assumed to be the default port of the received-protocol.
 
-   Multiple Via field values represent each proxy or gateway that has
+   Multiple Via field values represents each proxy or gateway that has
    forwarded the message. Each recipient MUST append its information
    such that the end result is ordered according to the sequence of
    forwarding applications.
@@ -6374,7 +6963,7 @@
    The request received by www.ics.uci.edu would then have the following
    Via header field:
 
Via: 1.0 fred, 1.1 nowhere.com (Apache/1.1)
 
    Proxies and gateways used as a portal through a network firewall
    SHOULD NOT, by default, forward the names and ports of hosts within
@@ -6388,123 +6977,148 @@
    Via header field entries with identical received-protocol values into
    a single such entry. For example,
 
Via: 1.0 ricky, 1.1 ethel, 1.1 fred, 1.0 lucy
 
could be collapsed to
 
Via: 1.0 ricky, 1.1 mertz, 1.0 lucy
 
    Applications SHOULD NOT combine multiple entries unless they are all
    under the same organizational control and the hosts have already been
    replaced by pseudonyms. Applications MUST NOT combine entries which
    have different received-protocol values.
 
-14.45 Warning
+14.46 Warning
 
-   The Warning response-header field is used to carry additional
+   The Warning general-header field is used to carry additional
-   information about the status of a response which may not
+   information about the status or transformation of a message which might not
-   be reflected by the response status code. This information is typically,
+   be reflected in the message. This information is typically
-   though not exclusively, used to warn about a possible lack of semantic
+   used to warn about a possible lack of semantic
-   transparency from caching operations.
+   transparency from caching operations
+   or transformations applied to the entity body of the message.
 
    Warning headers are sent with responses using:
 
Warning    = "Warning" ":" 1#warning-value
+
-          warning-value = warn-code SP warn-agent SP warn-text
+       warning-value = warn-code SP warn-agent SP warn-text
+                                             [SP warn-date]
 
-          warn-code  = 2DIGIT
+       warn-code  = 3DIGIT
warn-agent = ( host [ ":" port ] ) | pseudonym
; the name or pseudonym of the server adding
; the Warning header, for use in debugging
warn-text  = quoted-string
+       warn-date  = <"> HTTP-date <">
 
-   A response may carry more than one Warning header.
+   A response MAY carry more than one Warning header.
 
-   The warn-text should be in a natural language and character set that
+   The warn-text SHOULD be in a natural language and character set that
    is most likely to be intelligible to the human user receiving the response.
-    This decision may be based on any available knowledge,
+    This decision MAY be based on any available knowledge,
such as the location of the cache or user, the Accept-Language field in a
request, the Content-Language field in a response, etc.
The default language is English and the default character set is ISO-8859-1.
 
    If a character set other than ISO-8859-1 is used, it MUST be encoded
-   in the warn-text using the method described in RFC 1522 [14].
+   in the warn-text using the method described in RFC 2047 [14].
 
+   Warning headers can in general be applied to any message, however
+   some specific warn-codes are specific to caches and can only be
+   applied to response messages.
-   Any server or cache may add Warning headers to a response.
-   New Warning headers should be added
+   New Warning headers SHOULD be added
after any existing Warning headers. A cache MUST NOT delete any Warning header
-   that it received with a response. However, if a cache successfully validates a
+   that it received with a message. However, if a cache successfully validates a
cache entry, it SHOULD remove any Warning headers previously attached to that 
entry except as specified for specific Warning codes.
It MUST then add any Warning headers received in the validating response.
In other words, Warning headers are those that would be attached to
the most recent relevant response.
 
    When multiple Warning headers are attached to a response, the user
-   agent SHOULD display as many of them as possible, in the order that
+   agent ought to inform the user of as many of them as possible, in the order that
-   they appear in the response. If it is not possible to display all of
+   they appear in the response. If it is not possible to inform the user of all of
-   the warnings, the user agent should follow these heuristics:
+   the warnings, the user agent SHOULD follow these heuristics:
-
-     o  Warnings that appear early in the response take priority over
+      - Warnings that appear early in the response take priority over
those appearing later in the response.
-     o  Warnings in the user's preferred character set take priority
+      - Warnings in the user's preferred character set take priority
over warnings in other character sets but with identical warn-codes
and warn-agents.
 
-   Systems that generate multiple Warning headers should order them with
+   Systems that generate multiple Warning headers SHOULD order them with
    this user agent behavior in mind.
 
+   Requirements for the behavior of caches with respect to Warnings are
+   stated in section 13.1.2.
+
    This is a list of the currently-defined warn-codes, each with a
    recommended warn-text in English, and a description of its meaning.
 
-10 Response is stale
+   110 Response is stale
MUST be included whenever the returned response is stale.
-  A cache may add this warning to any response, but may never remove it until the
-  response is known to be fresh.
-
-11 Revalidation failed
+   111 Revalidation failed
MUST be included if a cache returns a stale response because an
attempt to revalidate the response failed, due to an inability to reach the server.
-  A cache may add this warning to any response, but
-  may never remove it until the response is successfully revalidated.
-
-12 Disconnected operation
+   112 Disconnected operation
SHOULD be included if the cache is intentionally disconnected from
the rest of the network for a period of time.
-
-13 Heuristic expiration
+   113 Heuristic expiration
MUST be included if the cache heuristically chose a freshness
lifetime greater than 24 hours and the response's age is greater
than 24 hours.
-
-14 Transformation applied
-  MUST be added by an intermediate cache or proxy if it applies any
-  transformation changing the content-coding (as specified in the
-  Content-Encoding header) or media-type (as specified in the
-  Content-Type header) of the response, unless this Warning code
-  already appears in the response. MUST NOT be deleted from a response
-  even after revalidation.
-
-99 Miscellaneous warning
+   199 Miscellaneous warning
-  The warning text may include arbitrary information to be presented
+     The warning text MAY include arbitrary information to be presented
to a human user, or logged. A system receiving this warning MUST NOT take any automated action
- .
+    , besides presenting the warning to the user.
+
+   214 Transformation applied
+     MUST be added by an intermediate cache or proxy if it applies any
+     transformation changing the content-coding (as specified in the
+     Content-Encoding header) or media-type (as specified in the
+     Content-Type header) of the response, or the entity-body of the
+     response, unless this Warning code already appears in the response.
+
+   299 Miscellaneous persistent warning
+     The warning text MAY include arbitrary information to be presented
+     to a human user, or logged. A system receiving this warning MUST
+     NOT take any automated action.
+
+   If an implementation sends a message with one or more Warning headers
+   whose version is HTTP/1.0 or lower, then the sender MUST include in
+   each warning-value a warn-date that matches the date in the response.
+
+   If an implementation receives a message with a warning-value that
+   includes a warn-date, and that warn-date is different from the Date
+   value in the response, then that warning-value MUST be deleted from
+   the message before storing, forwarding, or using it. (This prevents
+   bad consequences of naive caching of Warning header fields.) If all
+   of the warning-values are deleted for this reason, the Warning header
+   MUST be deleted as well.
 
-14.46 WWW-Authenticate
+14.47 WWW-Authenticate
 
    The WWW-Authenticate response-header field MUST be included in 401
    (Unauthorized) response messages. The field value consists of at
    least one challenge that indicates the authentication scheme(s) and
    parameters applicable to the Request-URI.
 
WWW-Authenticate  = "WWW-Authenticate" ":" 1#challenge
 
-   The HTTP access authentication process is described in section 11.
+   The HTTP access authentication process is described in "HTTP
+   Authentication: Basic and Digest Access Authentication" [43].
-   User agents MUST take special care in parsing the WWW-Authenticate
+   User agents are advised to take special care in parsing the WWW-Authenticate
-   field value if it contains more than one challenge, or if more than
+   field value as it might contain more than one challenge, or if more than
one WWW-Authenticate header field is provided,
-   since the contents of a challenge may itself contain a comma-separated list of
+   the contents of a challenge itself can contain a comma-separated list of
    authentication parameters.
 
 15 Security Considerations
@@ -6515,104 +7129,30 @@
    definitive solutions to the problems revealed, though it does make
    some suggestions for reducing security risks.
 
-15.1 Authentication of Clients
 
-   The Basic authentication scheme is not a secure method of user
-   authentication, nor does it in any way protect the entity, which is
-   transmitted in clear text across the physical network used as the
-   carrier. HTTP does not prevent additional authentication schemes and
-   encryption mechanisms from being employed to increase security or the
-   addition of enhancements (such as schemes to use one-time passwords)
-   to Basic authentication.
-
-   The most serious flaw in Basic authentication is that it results in
-   the essentially clear text transmission of the user's password over
-   the physical network. It is this problem which Digest Authentication
-   attempts to address.
-
-   Because Basic authentication involves the clear text transmission of
-   passwords it SHOULD never be used (without enhancements) to protect
-   sensitive or valuable information.
-
-   A common use of Basic authentication is for identification purposes
-   -- requiring the user to provide a user name and password as a means
-   of identification, for example, for purposes of gathering accurate
-   usage statistics on a server. When used in this way it is tempting to
-   think that there is no danger in its use if illicit access to the
-   protected documents is not a major concern. This is only correct if
-   the server issues both user name and password to the users and in
-   particular does not allow the user to choose his or her own password.
-   The danger arises because naive users frequently reuse a single
-   password to avoid the task of maintaining multiple passwords.
-
-   If a server permits users to select their own passwords, then the
-   threat is not only illicit access to documents on the server but also
-   illicit access to the accounts of all users who have chosen to use
-   their account password. If users are allowed to choose their own
-   password that also means the server must maintain files containing
-   the (presumably encrypted) passwords. Many of these may be the
-   account passwords of users perhaps at distant sites. The owner or
-   administrator of such a system could conceivably incur liability if
-   this information is not maintained in a secure fashion.
-
-   Basic Authentication is also vulnerable to spoofing by counterfeit
-   servers. If a user can be led to believe that he is connecting to a
-   host containing information protected by basic authentication when in
-   fact he is connecting to a hostile server or gateway then the
-   attacker can request a password, store it for later use, and feign an
-   error. This type of attack is not possible with Digest Authentication
-   [32]. Server implementers SHOULD guard against the possibility of
-   this sort of counterfeiting by gateways or CGI scripts. In particular
-   it is very dangerous for a server to simply turn over a connection to
-   a gateway since that gateway can then use the persistent connection
-   mechanism to engage in multiple transactions with the client while
-   impersonating the original server in a way that is not detectable by
-   the client.
-
-15.2 Offering a Choice of Authentication Schemes
-
-   An HTTP/1.1 server may return multiple challenges with a 401
-   (Authenticate) response, and each challenge may use a different
-
-   scheme.  The order of the challenges returned to the user agent is in
-   the order that the server would prefer they be chosen. The server
-   should order its challenges with the "most secure" authentication
-   scheme first. A user agent should choose as the challenge to be made
-   to the user the first one that the user agent understands.
-
-   When the server offers choices of authentication schemes using the
-   WWW-Authenticate header, the "security" of the authentication is only
-   as malicious user could capture the set of challenges and try to
-   authenticate him/herself using the weakest of the authentication
-   schemes. Thus, the ordering serves more to protect the user's
-   credentials than the server's information.
-
-   A possible man-in-the-middle (MITM) attack would be to add a weak
-   authentication scheme to the set of choices, hoping that the client
-   will use one that exposes the user's credentials (e.g. password). For
-   this reason, the client should always use the strongest scheme that
-   it understands from the choices accepted.
-
-   An even better MITM attack would be to remove all offered choices,
-   and to insert a challenge that requests Basic authentication. For
-   this reason, user agents that are concerned about this kind of attack
-   could remember the strongest authentication scheme ever requested by
-   a server and produce a warning message that requires user
-   confirmation before using a weaker one. A particularly insidious way
-   to mount such a MITM attack would be to offer a "free" proxy caching
-   service to gullible users.

-15.6 Personal Information
+15.1 Personal Information
 
HTTP clients are often privy to large amounts of personal information
(e.g. the user's name, location, mail address, passwords, encryption
keys, etc.), and SHOULD be very careful to prevent unintentional
leakage of this information via the HTTP protocol to other sources.
We very strongly recommend that a convenient interface be provided
for the user to control dissemination of such information, and that
designers and implementors be particularly careful in this area.
-   History shows that errors in this area are often both
+   History shows that errors in this area often create
serious security and/or privacy problems
-   , and often
+    and
generate highly adverse publicity for the implementor's company.

-15.3 Abuse of Server Log Information
+15.1.1 Abuse of Server Log Information
 
    A server is in the position to save personal data about a user's
-   requests which may identify their reading patterns or subjects of
+   requests which might identify their reading patterns or subjects of
    interest. This information is clearly confidential in nature and its
-   handling may be constrained by law in certain countries. People using
+   handling can be constrained by law in certain countries. People using
    the HTTP protocol to provide data are responsible for ensuring that
    such material is not distributed without the permission of any
    individuals that are identifiable by the published results.
 
-15.4 Transfer of Sensitive Information
+15.1.2 Transfer of Sensitive Information
 
    Like any generic data transfer protocol, HTTP cannot regulate the
    content of the data that is transferred, nor is there any a priori
@@ -6622,9 +7162,9 @@
    possible to the provider of that information. Four header fields are
    worth special mention in this context: Server, Via, Referer and From.
 
-   Revealing the specific software version of the server may allow the
+   Revealing the specific software version of the server might allow the
    server machine to become more vulnerable to attacks against software
-   that is known to contain security holes. Implementers SHOULD make the
+   that is known to contain security holes. Implementors SHOULD make the
    Server header field a configurable option.
 
    Proxies which serve as a portal through a network firewall SHOULD
@@ -6633,12 +7173,13 @@
    SHOULD remove, or replace with sanitized versions, any Via fields
    generated behind the firewall.
 
-   The Referer field allows reading patterns to be studied and reverse
+   The Referer header allows reading patterns to be studied and reverse
    links drawn. Although it can be very useful, its power can be abused
    if user details are not separated from the information contained in
    the Referer. Even when the personal information has been removed, the
-   Referer field may indicate a private document's URI whose
+   Referer header might indicate a private document's URI whose
publication would be inappropriate.
 
    The information sent in the From field might conflict with the user's
    privacy interests or their site's security policy, and hence it
@@ -6651,44 +7192,40 @@
    be provided for the user to enable or disable the sending of From and
    Referer information.
 
+   The User-Agent (section 14.43) or Server (section 14.38) header
+   fields can sometimes be used to determine that a specific client or
+   server have a particular security hole which might be exploited.
+   Unfortunately, this same information is often used for other valuable
+   purposes for which HTTP currently has no better mechanism.
+
+15.1.3 Encoding Sensitive Information in URI's
+
+   Because the source of a link might be private information or might
+   reveal an otherwise private information source, it is strongly
+   recommended that the user be able to select whether or not the
+   Referer field is sent. For example, a browser client could have a
+   toggle switch for browsing openly/anonymously, which would
+   respectively enable/disable the sending of Referer and From
+   information.
 
+   Clients SHOULD NOT include a Referer header field in a (non-secure)
+   HTTP request if the referring page was transferred with a secure
+   protocol.
 
+   Authors of services which use the HTTP protocol SHOULD NOT use GET
+   based forms for the submission of sensitive data, because this will
+   cause this data to be encoded in the Request-URI. Many existing
+   servers, proxies, and user agents will log the request URI in some
+   place where it might be visible to third parties. Servers can use
+   POST-based form submission instead
-
-15.7 Privacy Issues Connected to Accept Headers
+15.1.4 Privacy Issues Connected to Accept Headers
 
    Accept request-headers can reveal information about the user to all
    servers which are accessed. The Accept-Language header in particular
    can reveal information the user would consider to be of a private
    nature, because the understanding of particular languages is often
    strongly correlated to the membership of a particular ethnic group.
    User agents which offer the option to configure the contents of an
    Accept-Language header to be sent in every request are strongly
@@ -6697,7 +7234,7 @@
 
    An approach that limits the loss of privacy would be for a user agent
    to omit the sending of Accept-Language headers by default, and to ask
-   the user whether it should start sending Accept-Language headers to a
+   the user whether or not to start sending Accept-Language headers to a
    server if it detects, by looking for any Vary response-header fields
    generated by the server, that such sending could improve the quality
    of service.
@@ -6711,14 +7248,33 @@
    many users not behind a proxy, the network address of the host
    running the user agent will also serve as a long-lived user
    identifier. In environments where proxies are used to enhance
-   privacy, user agents should be conservative in offering accept
+   privacy, user agents ought to be conservative in offering accept
header configuration options to end users. As an extreme privacy measure,
proxies could filter the accept headers in relayed requests. General
purpose user agents which provide a high degree of header
-   configurability should warn users about the loss of privacy which can
+   configurability SHOULD warn users about the loss of privacy which can
    be involved.
 
-15.5 Attacks Based On File and Path Names
+15.2 Attacks Based On File and Path Names
Implementations of HTTP origin servers SHOULD be careful to restrict
the documents returned by HTTP requests to be only those that were
intended by the server administrators. If an HTTP server translates
HTTP URIs directly into file system calls, the server MUST take
special care not to serve files that were not intended to be
delivered to HTTP clients. For example, UNIX, Microsoft Windows, and
other operating systems use ".." as a path component to indicate a
directory level above the current one. On such a system, an HTTP
server MUST disallow any such construct in the Request-URI if it
would otherwise allow access to a resource outside those intended to
be accessible via the HTTP server. Similarly, files intended for
reference only internally to the server (such as access control
files, configuration files, and script code) MUST be protected from
inappropriate retrieval, since they might contain sensitive
information. Experience has shown that minor bugs in such HTTP server
implementations have turned into security risks.

-15.8 DNS Spoofing
+15.3 DNS Spoofing
 
    Clients using HTTP rely heavily on the Domain Name Service, and are
    thus generally prone to security attacks based on the deliberate
@@ -6730,10 +7286,10 @@
    confirmation of an IP number/DNS name association, rather than
    caching the result of previous host name lookups. Many platforms
    already can cache host name lookups locally when appropriate, and
-   they SHOULD be configured to do so. These lookups should be cached,
+   they SHOULD be configured to do so. It is proper for these lookups to be cached,
however, only when the TTL (Time To Live) information reported by the
name server makes it likely that the cached information will remain useful.

    If HTTP clients cache the results of host name lookups in order to
    achieve a performance improvement, they MUST observe the TTL
@@ -6741,7 +7297,7 @@
 
    If HTTP clients do not observe this rule, they could be spoofed when
    a previously-accessed server's IP address changes. As network
-   renumbering is expected to become increasingly common, the
+   renumbering is expected to become increasingly common [24], the
    possibility of this form of attack will grow. Observing this
    requirement thus reduces this potential security vulnerability.
 
@@ -6750,28 +7306,108 @@
    likelihood of a user's experiencing failure in accessing sites which
    use that strategy.
 
-15.9 Location Headers and Spoofing
+15.4 Location Headers and Spoofing
 
    If a single server supports multiple organizations that do not trust
-   one another, then it must check the values of Location and Content-
+   one another, then it MUST check the values of Location and Content-
    Location headers in responses that are generated under control of
    said organizations to make sure that they do not attempt to
    invalidate resources over which they have no authority.
 
+15.5 Content-Disposition Issues
+
+   RFC 1806 [35], from which the often implemented Content-Disposition
+   (see section 19.5.1) header in HTTP is derived, has a number of very
+   serious security considerations. Content-Disposition is not part of
+   the HTTP standard, but since it is widely implemented, we are
+   documenting its use and risks for implementors. See RFC 2183 [49]
+   (which updates RFC 1806) for details.
+
+15.6 Authentication Credentials and Idle Clients
+
+   Existing HTTP clients and user agents typically retain authentication
+   information indefinitely. HTTP/1.1. does not provide a method for a
+   server to direct clients to discard these cached credentials. This is
+   a significant defect that requires further extensions to HTTP.
+   Circumstances under which credential caching can interfere with the
+   application's security model include but are not limited to:
+
+      - Clients which have been idle for an extended period following
+        which the server might wish to cause the client to reprompt the
+        user for credentials.
+
+      - Applications which include a session termination indication
+        (such as a `logout' or `commit' button on a page) after which
+        the server side of the application `knows' that there is no
+        further reason for the client to retain the credentials.
+
+   This is currently under separate study. There are a number of work-
+   arounds to parts of this problem, and we encourage the use of
+   password protection in screen savers, idle time-outs, and other
+   methods which mitigate the security problems inherent in this
+   problem. In particular, user agents which cache credentials are
+   encouraged to provide a readily accessible mechanism for discarding
+   cached credentials under user control.
+
+15.7 Proxies and Caching
+
+   By their very nature, HTTP proxies are men-in-the-middle, and
+   represent an opportunity for man-in-the-middle attacks. Compromise of
+   the systems on which the proxies run can result in serious security
+   and privacy problems. Proxies have access to security-related
+   information, personal information about individual users and
+   organizations, and proprietary information belonging to users and
+   content providers. A compromised proxy, or a proxy implemented or
+   configured without regard to security and privacy considerations,
+   might be used in the commission of a wide range of potential attacks.
+
+   Proxy operators should protect the systems on which proxies run as
+   they would protect any system that contains or transports sensitive
+   information. In particular, log information gathered at proxies often
+   contains highly sensitive personal information, and/or information
+   about organizations. Log information should be carefully guarded, and
+   appropriate guidelines for use developed and followed. (Section
+   15.1.1).
+
+   Caching proxies provide additional potential vulnerabilities, since
+   the contents of the cache represent an attractive target for
+   malicious exploitation. Because cache contents persist after an HTTP
+   request is complete, an attack on the cache can reveal information
+   long after a user believes that the information has been removed from
+   the network. Therefore, cache contents should be protected as
+   sensitive information.
+
+   Proxy implementors should consider the privacy and security
+   implications of their design and coding decisions, and of the
+   configuration options they provide to proxy operators (especially the
+   default configuration).
+
+   Users of a proxy need to be aware that they are no trustworthier than
+   the people who run the proxy; HTTP itself cannot solve this problem.
+
+   The judicious use of cryptography, when appropriate, may suffice to
+   protect against a broad range of security and privacy attacks. Such
+   cryptography is beyond the scope of the HTTP/1.1 specification.
+
+15.7.1 Denial of Service Attacks on Proxies
+
+   They exist. They are hard to defend against. Research continues.
+   Beware.
+
 16 Acknowledgments
 
    This specification makes heavy use of the augmented BNF and generic
-   constructs defined by David H. Crocker for RFC 822. Similarly, it
+   constructs defined by David H. Crocker for RFC 822 [9]. Similarly, it
    reuses many of the definitions provided by Nathaniel Borenstein and
-   Ned Freed for MIME. We hope that their inclusion in this
+   Ned Freed for MIME [7]. We hope that their inclusion in this
    specification will help reduce past confusion over the relationship
    between HTTP and Internet mail message formats.
 
-   The HTTP protocol has evolved considerably over the past four years.
+   The HTTP protocol has evolved considerably over the years.
-   It has benefited from a large and active developer community--the
+   It has benefited from a large and active developer community--the many
-   many people who have participated on the www-talk mailing list--and
+   people who have participated on the www-talk mailing list--and
it is that community which has been most responsible for the success of
HTTP and of the World-Wide Web in general. Marc Andreessen, Robert
    Cailliau, Daniel W. Connolly, Bob Denny, John Franks, Jean-Francois
    Groff, Phillip M. Hallam-Baker, Hakon W. Lie, Ari Luotonen, Rob
    McCool, Lou Montulli, Dave Raggett, Tony Sanders, and Marc
@@ -6782,32 +7418,32 @@
    participating in the HTTP-WG. In addition to those already mentioned,
    the following individuals have contributed to this specification:
 
-          Gary Adams                  Albert Lunde
+       Gary Adams                  Ross Patterson
-          Harald Tveit Alvestrand     John C. Mallery
+       Harald Tveit Alvestrand     Albert Lunde
-          Keith Ball                  Jean-Philippe Martin-Flatin
+       Keith Ball                  John C. Mallery
-          Brian Behlendorf            Larry Masinter
+       Brian Behlendorf            Jean-Philippe Martin-Flatin
Paul Burchard               Mitra
Maurizio Codogno            David Morris
Mike Cowlishaw              Gavin Nicol
Roman Czyborra              Bill Perry
Michael A. Dolan            Jeffrey Perry
David J. Fiander            Scott Powers
Alan Freier                 Owen Rees
Marc Hedlund                Luigi Rizzo
Greg Herlihy                David Robinson
Koen Holtman                Marc Salomon
Alex Hopmann                Rich Salz
Bob Jernigan                Allan M. Schiffman
Shel Kaphan                 Jim Seidman
Rohit Khare                 Chuck Shotton
John Klensin                Eric W. Sink
Martijn Koster              Simon E. Spero
Alexei Kosut                Richard N. Taylor
David M. Kristol            Robert S. Thau
Daniel LaLiberte            Bill (BearHeart) Weinman
Ben Laurie                  Francois Yergeau
Paul J. Leach               Mary Ellen Zurko
-          Daniel DuBois
+       Daniel DuBois               Josh Cohen
 
    Much of the content and presentation of the caching design is due to
    suggestions and comments from individuals including: Shel Kaphan,
@@ -6822,150 +7458,210 @@
    Jim Gettys (the current editor of this document) wishes particularly
    to thank Roy Fielding, the previous editor of this document, along
    with John Klensin, Jeff Mogul, Paul Leach, Dave Kristol, Koen
-   Holtman, John Franks, Alex Hopmann, and Larry Masinter for their help.
+   Holtman, John Franks, Josh Cohen, Alex Hopmann, Scott Lawrence, and
+   Larry Masinter for their help. And thanks go particularly to Jeff
+   Mogul and Scott Lawrence for performing the "MUST/MAY/SHOULD" audit.
+
+   The Apache Group, Anselm Baird-Smith, author of Jigsaw, and Henrik
+   Frystyk implemented RFC 2068 early, and we wish to thank them for the
+   discovery of many of the problems that this document attempts to
+   rectify.
 
 17 References
 
-   [1] Alvestrand, H., "Tags for the identification of languages", RFC
+   [1] Alvestrand, H., "Tags for the Identification of Languages", RFC
-   1766, UNINETT, March 1995.
+       1766, March 1995.
 
    [2] Anklesaria, F., McCahill, M., Lindner, P., Johnson, D., Torrey,
-   D., and B. Alberti. "The Internet Gopher Protocol: (a distributed
+       D. and B. Alberti, "The Internet Gopher Protocol (a distributed
-   document search and retrieval protocol)", RFC 1436, University of
+       document search and retrieval protocol)", RFC 1436, March 1993.
-   Minnesota, March 1993.
-
-   [3] Berners-Lee, T., "Universal Resource Identifiers in WWW", A
-   Unifying Syntax for the Expression of Names and Addresses of Objects
-   on the Network as used in the World-Wide Web", RFC 1630, CERN, June
-   1994.
+   [3] Berners-Lee, T., "Universal Resource Identifiers in WWW", RFC
+       1630, June 1994.
-
-   [4] Berners-Lee, T., Masinter, L., and M. McCahill, "Uniform Resource
-   Locators (URL)", RFC 1738, CERN, Xerox PARC, University of Minnesota,
-   December 1994.
+   [4] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
+       Locators (URL)", RFC 1738, December 1994.
-
-   [5] Berners-Lee, T., and D. Connolly, "HyperText Markup Language
-   Specification - 2.0", RFC 1866, MIT/LCS, November 1995.
+   [5] Berners-Lee, T. and D. Connolly, "Hypertext Markup Language -
+       2.0", RFC 1866, November 1995.
-
-   [6] Berners-Lee, T., Fielding, R., and H. Frystyk, "Hypertext
-   Transfer Protocol -- HTTP/1.0.", RFC 1945 MIT/LCS, UC Irvine, May
-   1996.
+   [6] Berners-Lee, T., Fielding, R. and H. Frystyk, "Hypertext Transfer
+       Protocol -- HTTP/1.0", RFC 1945, May 1996.
-
-   [7] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
-   Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
-   2045, Innosoft, First Virtual, November 1996.
+   [7] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
+       Extensions (MIME) Part One: Format of Internet Message Bodies",
+       RFC 2045, November 1996.
 
-   [8] Braden, R., "Requirements for Internet hosts - application and
-   support", STD 3,  RFC 1123, IETF, October 1989.
+   [8] Braden, R., "Requirements for Internet Hosts -- Communication
+       Layers", STD 3, RFC 1123, October 1989.
 
-   [9] Crocker, D., "Standard for the Format of ARPA Internet Text
-   Messages", STD 11, RFC 822, UDEL, August 1982.
+   [9] Crocker, D., "Standard for The Format of ARPA Internet Text
+       Messages", STD 11, RFC 822, August 1982.
 
    [10] Davis, F., Kahle, B., Morris, H., Salem, J., Shen, T., Wang, R.,
-   Sui, J., and M. Grinbaum. "WAIS Interface Protocol Prototype
-   Functional Specification", (v1.5), Thinking Machines Corporation,
-   April 1990.
+        Sui, J., and M. Grinbaum, "WAIS Interface Protocol Prototype
+        Functional Specification," (v1.5), Thinking Machines
+        Corporation, April 1990.
-
-   [11] Fielding, R., "Relative Uniform Resource Locators", RFC 1808, UC
-   Irvine, June 1995.
+   [11] Fielding, R., "Relative Uniform Resource Locators", RFC 1808,
+        June 1995.
-
-   [12] Horton, M., and R. Adams. "Standard for interchange of USENET
-   messages", RFC 1036, AT&T Bell Laboratories, Center for Seismic
-   Studies, December 1987.
+   [12] Horton, M. and R. Adams, "Standard for Interchange of USENET
+        Messages", RFC 1036, December 1987.
-
-   [13] Kantor, B., and P. Lapsley. "Network News Transfer Protocol." A
-   Proposed Standard for the Stream-Based Transmission of News", RFC
-   977, UC San Diego, UC Berkeley, February 1986.
+   [13] Kantor, B. and P. Lapsley, "Network News Transfer Protocol", RFC
+        977, February 1986.
 
    [14] Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part
-   Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
-   University of Tennessee, November 1996.
+        Three: Message Header Extensions for Non-ASCII Text", RFC 2047,
+        November 1996.
 
-   [15] Nebel, E., and L. Masinter. "Form-based File Upload in HTML",
-   RFC 1867, Xerox Corporation, November 1995.
+   [15] Nebel, E. and L. Masinter, "Form-based File Upload in HTML", RFC
+        1867, November 1995.
 
    [16] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
-   USC/ISI, August 1982.
+        August 1982.
 
-   [17] Postel, J., "Media Type Registration Procedure", RFC 2048,
-   USC/ISI, November 1996.
+   [17] [DEL[Postel, J., "Media Type Registration Procedure", RFC 1590]]
[INS[[INS[{errata}]] Freed, N., Klensin, J., and Postel, J., "Mulitpurpose Internet Mail
        Extensions (MIME) Part Four: Registration Procedure", RFC 2048]],
+        November 1996.
 
-   [18] Postel, J., and J. Reynolds, "File Transfer Protocol (FTP)", STD
-   9, RFC 959, USC/ISI, October 1985.
+   [18] Postel, J. and J. Reynolds, "File Transfer Protocol", STD 9, RFC
+        959, October 1985.
 
-   [19] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC
-   1700, USC/ISI, October 1994.
+   [19] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2, RFC 1700,
+        October 1994.
 
-   [20] Sollins, K., and L. Masinter, "Functional Requirements for
-   Uniform Resource Names", RFC 1737, MIT/LCS, Xerox Corporation,
-   December 1994.
+   [20] Sollins, K. and L. Masinter, "Functional Requirements for
+        Uniform Resource Names", RFC 1737, December 1994.
 
    [21] US-ASCII. Coded Character Set - 7-Bit American Standard Code for
-   Information Interchange. Standard ANSI X3.4-1986, ANSI, 1986.
+        Information Interchange. Standard ANSI X3.4-1986, ANSI, 1986.
 
    [22] ISO-8859. International Standard -- Information Processing --
8-bit Single-Byte Coded Graphic Character Sets --
-     Part 1: Latin alphabet No. 1, ISO 8859-1:1987.
-     Part 2: Latin alphabet No. 2, ISO 8859-2, 1987.
-     Part 3: Latin alphabet No. 3, ISO 8859-3, 1988.
-     Part 4: Latin alphabet No. 4, ISO 8859-4, 1988.
-     Part 5: Latin/Cyrillic alphabet, ISO 8859-5, 1988.
-     Part 6: Latin/Arabic alphabet, ISO 8859-6, 1987.
-     Part 7: Latin/Greek alphabet, ISO 8859-7, 1987.
-     Part 8: Latin/Hebrew alphabet, ISO 8859-8, 1988.
-     Part 9: Latin alphabet No. 5, ISO 8859-9, 1990.
+        Part 1: Latin alphabet No. 1, ISO-8859-1:1987.
+        Part 2: Latin alphabet No. 2, ISO-8859-2, 1987.
+        Part 3: Latin alphabet No. 3, ISO-8859-3, 1988.
+        Part 4: Latin alphabet No. 4, ISO-8859-4, 1988.
+        Part 5: Latin/Cyrillic alphabet, ISO-8859-5, 1988.
+        Part 6: Latin/Arabic alphabet, ISO-8859-6, 1987.
+        Part 7: Latin/Greek alphabet, ISO-8859-7, 1987.
+        Part 8: Latin/Hebrew alphabet, ISO-8859-8, 1988.
+        Part 9: Latin alphabet No. 5, ISO-8859-9, 1990.
-
-   [23] Meyers, J., and M. Rose "The Content-MD5 Header Field", RFC
-   1864, Carnegie Mellon, Dover Beach Consulting, October, 1995.
+   [23] Meyers, J. and M. Rose, "The Content-MD5 Header Field", RFC
+        1864, October 1995.
-
-   [24] Carpenter, B., and Y. Rekhter, "Renumbering Needs Work", RFC
-   1900, IAB, February 1996.
+   [24] Carpenter, B. and Y. Rekhter, "Renumbering Needs Work", RFC
+        1900, February 1996.
-
-   [25] Deutsch, P., "GZIP file format specification version 4.3." RFC
-   1952, Aladdin Enterprises, May 1996.
+   [25] Deutsch, P., "GZIP file format specification version 4.3", RFC
+        1952, May 1996.
-
-   [26] Venkata N. Padmanabhan and Jeffrey C. Mogul. Improving HTTP
-   Latency. Computer Networks and ISDN Systems, v. 28, pp. 25-35, Dec.
-   1995.  Slightly revised version of paper in Proc. 2nd International
-   WWW Conf. '94: Mosaic and the Web, Oct. 1994, which is available at
-   http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/
-   HTTPLatency.html.
+   [26] Venkata N. Padmanabhan, and Jeffrey C. Mogul. "Improving HTTP
+        Latency", Computer Networks and ISDN Systems, v. 28, pp. 25-35,
+        Dec. 1995. Slightly revised version of paper in Proc. 2nd
+        International WWW Conference '94: Mosaic and the Web, Oct. 1994,
+        which is available at
+        http://www.ncsa.uiuc.edu/SDG/IT94/Proceedings/DDay/mogul/HTTPLat
+        ency.html.
-
-   [27] Joe Touch, John Heidemann, and Katia Obraczka, "Analysis of HTTP
-   Performance", <URL: http://www.isi.edu/lsam/ib/http-perf/>,
-   USC/Information Sciences Institute, June 1996
+   [27] Joe Touch, John Heidemann, and Katia Obraczka. "Analysis of HTTP
+        Performance", <URL: http://www.isi.edu/touch/pubs/http-perf96/>,
+        ISI Research Report ISI/RR-98-463, (original report dated Aug.
+        1996), USC/Information Sciences Institute, August 1998.
-
-   [28] Mills, D., "Network Time Protocol, Version 3, Specification,
-   Implementation and Analysis", RFC 1305, University of Delaware, March
-   1992.
+   [28] Mills, D., "Network Time Protocol (Version 3) Specification,
+        Implementation and Analysis", RFC 1305, March 1992.
 
    [29] Deutsch, P., "DEFLATE Compressed Data Format Specification
-   version 1.3." RFC 1951, Aladdin Enterprises, May 1996.
+        version 1.3", RFC 1951, May 1996.
 
-   [30] Spero, S., "Analysis of HTTP Performance Problems"
-   <URL:http://sunsite.unc.edu/mdma-release/http-prob.html>.
+   [30] S. Spero, "Analysis of HTTP Performance Problems,"
+        http://sunsite.unc.edu/mdma-release/http-prob.html.
 
-   [31] Deutsch, P., and J-L. Gailly, "ZLIB Compressed Data Format
-   Specification version 3.3", RFC 1950, Aladdin Enterprises, Info-ZIP,
-   May 1996.
+   [31] Deutsch, P. and J. Gailly, "ZLIB Compressed Data Format
+        Specification version 3.3", RFC 1950, May 1996.
 
    [32] Franks, J., Hallam-Baker, P., Hostetler, J., Leach, P.,
-   Luotonen, A., Sink, E., and L. Stewart, "An Extension to HTTP :
-   Digest Access Authentication", RFC 2069, January 1997.
+        Luotonen, A., Sink, E. and L. Stewart, "An Extension to HTTP:
+        Digest Access Authentication", RFC 2069, January 1997.
+
+   [33] Fielding, R., Gettys, J., Mogul, J., Frystyk, H. and T.
+        Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1", RFC
+        2068, January 1997.
+
+   [34] Bradner, S., "Key words for use in RFCs to Indicate Requirement
+        Levels", BCP 14, RFC 2119, March 1997.
+
+   [35] Troost, R. and Dorner, S., "Communicating Presentation
+        Information in Internet Messages: The Content-Disposition
+        Header", RFC 1806, June 1995.
+
+   [36] Mogul, J., Fielding, R., Gettys, J. and H. Frystyk, "Use and
+        Interpretation of HTTP Version Numbers", RFC 2145, May 1997.
+        [DEL[ [jg639] ]]
+
+   [37] Palme, J., "Common Internet Message Headers", RFC 2076, February
+        1997. [DEL[ [jg640] ]]
+
+   [38] Yergeau, F., "UTF-8, a transformation format of Unicode and
+        ISO-10646", RFC 2279, January 1998. [DEL[ [jg641] ]]
+
+   [39] Nielsen, H.F., Gettys, J., Baird-Smith, A., Prud'hommeaux, E.,
+        Lie, H., and C. Lilley. "Network Performance Effects of
+        HTTP/1.1, CSS1, and PNG," Proceedings of ACM SIGCOMM '97, Cannes
+        France, September 1997.[DEL[ [jg642] ]]
+
+   [40] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
+        Extensions (MIME) Part Two: Media Types", RFC 2046, November
+        1996. [DEL[ [jg643] ]]
+
+   [41] Alvestrand, H., "IETF Policy on Character Sets and Languages",
+        BCP 18, RFC 2277, January 1998. [DEL[ [jg644] ]]
+
+   [42] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
+        Identifiers (URI): Generic Syntax and Semantics", RFC 2396,
+        August 1998. [DEL[ [jg645] ]]
+
+   [43] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
+        Leach, P., Luotonen, A., Sink, E. and L. Stewart, "HTTP
+        Authentication: Basic and Digest Access Authentication", RFC
+        2617, June 1999. [DEL[ [jg646] ]]
 
+   [44] Luotonen, A., "Tunneling TCP based protocols through Web proxy
+        servers," Work in Progress. [DEL[ [jg647] ]]

[INS[{[jg64*]s are removed by errata}]]
+
+   [45] Palme, J. and A. Hopmann, "MIME E-mail Encapsulation of
+        Aggregate Documents, such as HTML (MHTML)", RFC 2110, March
+        1997.
+
+   [46] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
+        9, RFC 2026, October 1996.
+
+   [47] Masinter, L., "Hyper Text Coffee Pot Control Protocol
+        (HTCPCP/1.0)", RFC 2324, 1 April 1998.
+
+   [48] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
+        Extensions (MIME) Part Five: Conformance Criteria and Examples",
+        RFC 2049, November 1996.
+
+   [49] Troost, R., Dorner, S. and K. Moore, "Communicating Presentation
+        Information in Internet Messages: The Content-Disposition Header
+        Field", RFC 2183, August 1997.
 
 18 Authors' Addresses
 
    Roy T. Fielding
-   Department of Information and Computer Science
+   Information and Computer Science
-   University of California
+   University of California, Irvine
-   Irvine, CA 92717-3425, USA
+   Irvine, CA 92697-3425, USA
 
-   Fax: +1 (714) 824-4056
+   Fax: +1 (949) 824-1715
    EMail: fielding@ics.uci.edu
 
-   Jim Gettys
+   James Gettys
+   World Wide Web Consortium
    MIT Laboratory for Computer Science
    545 Technology Square
    Cambridge, MA 02139, USA
@@ -6975,14 +7671,14 @@
 
    Jeffrey C. Mogul
    Western Research Laboratory
-   Digital Equipment Corporation
+   Compaq Computer Corporation
    250 University Avenue
    Palo Alto, California, 94305, USA
 
    EMail: mogul@wrl.dec.com
 
    Henrik Frystyk Nielsen
-   W3 Consortium
+   World Wide Web Consortium
    MIT Laboratory for Computer Science
    545 Technology Square
    Cambridge, MA 02139, USA
@@ -6990,8 +7686,22 @@
    Fax: +1 (617) 258 8682
    EMail: frystyk@w3.org
 
+   Larry Masinter
+   Xerox Corporation
+   3333 Coyote Hill Road
+   Palo Alto, CA 94034, USA
+
+   EMail: masinter@parc.xerox.com
+
+   Paul J. Leach
+   Microsoft Corporation
+   1 Microsoft Way
+   Redmond, WA 98052, USA
+
+   EMail: paulle@microsoft.com
+
    Tim Berners-Lee
-   Director, W3 Consortium
+   Director, World Wide Web Consortium
    MIT Laboratory for Computer Science
    545 Technology Square
    Cambridge, MA 02139, USA
@@ -7001,57 +7711,73 @@
 
 19 Appendices
 
-19.1 Internet Media Type message/http
+19.1 Internet Media Type message/http and application/http
 
    In addition to defining the HTTP/1.1 protocol, this document serves
-   as the specification for the Internet media type "message/http".
+   as the specification for the Internet media type "message/http" and
+   "application/http". The message/http type can be used to enclose a
+   single HTTP request or response message, provided that it obeys the
+   MIME restrictions for all "message" types regarding line length and
+   encodings. The application/http type can be used to enclose a
+   pipeline of one or more HTTP request or response messages (not intermixed).
-   The following is to be registered with IANA.
+   The following is to be registered with IANA [17].
 
        Media Type name:         message
        Media subtype name:      http
        Required parameters:     none
        Optional parameters:     version, msgtype
-
         version: The HTTP-Version number of the enclosed message
                  (e.g., "1.1"). If not present, the version can be
                  determined from the first line of the body.
-
         msgtype: The message type -- "request" or "response". If not
                  present, the type can be determined from the first
                  line of the body.
-
        Encoding considerations: only "7bit", "8bit", or "binary" are
                                 permitted
        Security considerations: none
 
+       Media Type name:         application
+       Media subtype name:      http
+       Required parameters:     none
+       Optional parameters:     version, msgtype
+        version: The HTTP-Version number of the enclosed messages
+                 (e.g., "1.1"). If not present, the version can be
+                 determined from the first line of the body.
+        msgtype: The message type -- "request" or "response". If not
+                 present, the type can be determined from the first
+                 line of the body.
+       Encoding considerations: HTTP messages enclosed by this type
+                 are in "binary" format; use of an appropriate
+                 Content-Transfer-Encoding is required when
+                 transmitted via E-mail.
+       Security considerations: none
 
 19.2 Internet Media Type multipart/byteranges
 
-   When an HTTP message includes the
+   When an HTTP 206 (Partial Content) response message includes the
-   content of multiple ranges (for example, a response to a request for multiple
+   content of multiple ranges (a response to a request for multiple
-   non-overlapping ranges), these are transmitted as a multipart
+   non-overlapping ranges), these are transmitted as a multipart
-   MIME message. The multipart
+   message-body. The
    media type for this purpose is called "multipart/byteranges".
 
    The multipart/byteranges media type includes two or more parts, each
with its own Content-Type and Content-Range fields.
-   The parts are separated using a MIME boundary parameter.
+   The required boundary parameter specifies the boundary string used to separate
+   each body-part.
-
Media Type name:         multipart
Media subtype name:      byteranges
Required parameters:     boundary
Optional parameters:     none
Encoding considerations: only "7bit", "8bit", or "binary" are permitted
Security considerations: none
 
For example:
 
-   HTTP/1.1 206 Partial content
+   HTTP/1.1 206 Partial Content
    Date: Wed, 15 Nov 1995 06:25:24 GMT
-   Last-modified: Wed, 15 Nov 1995 04:58:08 GMT
+   Last-Modified: Wed, 15 Nov 1995 04:58:08 GMT
    Content-type: multipart/byteranges; boundary=THIS_STRING_SEPARATES
 
    --THIS_STRING_SEPARATES
@@ -7066,6 +7792,20 @@
    ...the second range
    --THIS_STRING_SEPARATES--
 
+      Notes:
+
+      1) Additional CRLFs may precede the first boundary string in the
+         entity.
+
+      2) Although RFC 2046 [40] permits the boundary string to be
+         quoted, some existing implementations handle a quoted boundary
+         string incorrectly.
+
+      3) A number of browsers and servers were coded to an early draft
+         of the byteranges specification to use a media type of
+         multipart/x-byteranges, which is almost, but not quite
+         compatible with the version documented in HTTP/1.1.
+
 19.3 Tolerant Applications
 
    Although this document specifies the requirements for the generation
@@ -7083,72 +7823,96 @@
    However, we recommend that applications, when parsing such headers,
    recognize a single LF as a line terminator and ignore the leading CR.
 
-   The character set of an entity-body should be labeled as the lowest
+   The character set of an entity-body SHOULD be labeled as the lowest
    common denominator of the character codes used within that body, with
-   the exception that no label is preferred over
+   the exception that not labeling the entity is preferred over labeling
-   the labels US-ASCII or ISO-8859-1.
+   the entity with the labels US-ASCII or ISO-8859-1. See section 3.7.1 and 3.4.1.
 
    Additional rules for requirements on parsing and encoding of dates
    and other potential problems with date encodings include:
 
-  o  HTTP/1.1 clients and caches should assume that an RFC-850 date
+   - HTTP/1.1 clients and caches SHOULD assume that an RFC-850 date
which appears to be more than 50 years in the future is in fact
in the past (this helps solve the "year 2000" problem).
-
-  o  An HTTP/1.1 implementation may internally represent a parsed
+   - An HTTP/1.1 implementation MAY internally represent a parsed
Expires date as earlier than the proper value, but MUST NOT
internally represent a parsed Expires date as later than the proper value.
-
-  o  All expiration-related calculations must be done in GMT. The
+   - All expiration-related calculations MUST be done in GMT. The
local time zone MUST NOT influence the calculation or comparison
of an age or expiration time.
-
-  o  If an HTTP header incorrectly carries a date value with a time
+   - If an HTTP header incorrectly carries a date value with a time
-     zone other than GMT, it must
+     zone other than GMT, it MUST
be converted into GMT using the most conservative possible conversion.
 
-19.4 Differences Between HTTP Entities and MIME Entities
+19.4 Differences Between HTTP Entities and RFC 2045 Entities
 
    HTTP/1.1 uses many of the constructs defined for Internet Mail (RFC
-   822) and the Multipurpose Internet Mail Extensions (MIME ) to
+   822 [9]) and the Multipurpose Internet Mail Extensions (MIME [7]) to
allow entities to be transmitted in an open variety of
-   representations and with extensible mechanisms. However, MIME [7] discusses
+   representations and with extensible mechanisms. However, RFC 2045 discusses
mail, and HTTP has a few features that are different from
-   those described in MIME.  These differences were carefully chosen
+   those described in RFC 2045. These differences were carefully chosen
to optimize performance over binary connections, to allow greater
freedom in the use of new media types, to make date comparisons easier, and to
acknowledge the practice of some early HTTP servers and clients.

-   This appendix describes specific areas where HTTP differs from MIME.
+   This appendix describes specific areas where HTTP differs from RFC 2045.
Proxies and gateways to strict MIME environments SHOULD be aware of
these differences and provide the appropriate conversions where
necessary. Proxies and gateways from MIME environments to HTTP also
need to be aware of the differences because some conversions
-   may be required.
+   might be required.
-
-19.4.7 MIME-Version
+19.4.1 MIME-Version

-   HTTP is not a MIME-compliant protocol (see appendix 19.4).
+   HTTP is not a MIME-compliant protocol.
-   However, HTTP/1.1 messages may include a single MIME-Version general-header
+   However, HTTP/1.1 messages MAY include a single MIME-Version general-header
field to indicate what version of the MIME protocol was used to construct the
message. Use of the MIME-Version header field indicates that the message
-   is in full compliance with the MIME protocol.
+   is in full compliance with the MIME protocol (as defined in RFC 2045[7]).
Proxies/gateways are responsible for ensuring full compliance (where
possible) when exporting HTTP messages to strict MIME environments.

MIME-Version   = "MIME-Version" ":" 1*DIGIT "." 1*DIGIT

MIME version "1.0" is the default for use in HTTP/1.1. However,
HTTP/1.1 message parsing and semantics are defined by this document
and not the MIME specification.

-19.4.1 Conversion to Canonical Form
+19.4.2 Conversion to Canonical Form
-
-   MIME requires that an Internet mail entity be converted to
+   RFC 2045 [7] requires that an Internet mail entity be converted to
-   canonical form prior to being transferred.  Section 3.7.1 of this document
+   canonical form prior to being transferred, as described in section 4
+   of RFC 2049 [48]. Section 3.7.1 of this document
describes the forms allowed for subtypes of the "text" media type when
-   transmitted over HTTP. MIME requires that content with a type of "text"
+   transmitted over HTTP. RFC 2046 requires that content with a type of "text"
represent line breaks as CRLF and forbids the use of CR or LF outside of
line break sequences. HTTP allows CRLF, bare CR, and bare LF to indicate a
line break within text content when a message is
transmitted over HTTP.
 
    Where it is possible, a proxy or gateway from HTTP to a strict MIME
    environment SHOULD translate all line breaks within the text media
-   types described in section 3.7.1 of this document to the MIME
+   types described in section 3.7.1 of this document to the RFC 2049
-   canonical form of CRLF. Note, however, that this may be complicated
+   canonical form of CRLF. Note, however, that this might be complicated
    by the presence of a Content-Encoding and by the fact that HTTP
    allows the use of some character sets which do not use octets 13 and
    10 to represent CR and LF, as is the case for some multi-byte
    character sets.
 
+   Implementors should note that conversion will break any cryptographic
+   checksums applied to the original content unless the original content
+   is already in canonical form. Therefore, the canonical form is
+   recommended for any content that uses such checksums in HTTP.
+
-19.4.2 Conversion of Date Formats
+19.4.3 Conversion of Date Formats
 
    HTTP/1.1 uses a restricted set of date formats (section 3.3.1) to
    simplify the process of date comparison. Proxies and gateways from
@@ -7156,88 +7920,154 @@
    message conforms to one of the HTTP/1.1 formats and rewrite the date
    if necessary.
 
-19.4.3 Introduction of Content-Encoding
+19.4.4 Introduction of Content-Encoding
 
-   MIME does not include any concept equivalent to HTTP/1.1's 
+   RFC 2045 does not include any concept equivalent to HTTP/1.1's
Content-Encoding header field. Since this acts as a modifier on the
media type, proxies and gateways from HTTP to MIME-compliant protocols MUST
either change the value of the Content-Type headerfield or decode
the entity-body before forwarding the message. (Some experimental
applications of Content-Type for Internet mail have used a media-type
parameter of ";conversions=<content-coding>" to perform
-   an equivalent function as Content-Encoding. However, this parameter is not part of
+   a function equivalent to Content-Encoding. However, this parameter is not part of
-   MIME.)
+   RFC 2045.)
 
-19.4.4 No Content-Transfer-Encoding
+19.4.5 No Content-Transfer-Encoding
 
-   HTTP does not use the Content-Transfer-Encoding (CTE) field of MIME.
+   HTTP does not use the Content-Transfer-Encoding (CTE) field of RFC 2045.
Proxies and gateways from MIME-compliant protocols to HTTP MUST
    remove any [DEL[non-identity]] CTE [DEL[("quoted-printable" or "base64")]] encoding [INS[{ammended by errata}]]
    prior to delivering the response message to an HTTP client.
 
    Proxies and gateways from HTTP to MIME-compliant protocols are
    responsible for ensuring that the message is in the correct format
    and encoding for safe transport on that protocol, where "safe
    transport" is defined by the limitations of the protocol being used.
    Such a proxy or gateway SHOULD label the data with an appropriate
    Content-Transfer-Encoding if doing so will improve the likelihood of
    safe transport over the destination protocol.
 
-19.4.5 HTTP Header Fields in Multipart Body-Parts
-
-   In MIME, most header fields in multipart body-parts are generally
-   ignored unless the field name begins with "Content-". In HTTP/1.1,
-   multipart body-parts may contain any HTTP header fields which are
-   significant to the meaning of that part.
-
 19.4.6 Introduction of Transfer-Encoding
 
    HTTP/1.1 introduces the Transfer-Encoding header field (section
-   14.40).  Proxies/gateways MUST remove any transfer coding prior to
+   14.41). Proxies/gateways MUST remove any transfer-coding prior to
    forwarding a message via a MIME-compliant protocol.
 
-   A process for decoding the "chunked" transfer coding (section 3.6)
+   A process for decoding the "chunked" transfer-coding (section 3.6)
    can be represented in pseudo-code as:
 
length := 0
-          read chunk-size, chunk-ext (if any) and CRLF
+       read chunk-size, chunk-extension (if any) and CRLF
while (chunk-size > 0) {
read chunk-data and CRLF
append chunk-data to entity-body
length := length + chunk-size
read chunk-size and CRLF
}
read entity-header
while (entity-header not empty) {
append entity-header to existing header fields
read entity-header
}
Content-Length := length
Remove "chunked" from Transfer-Encoding
-
-
+
+19.4.7 MHTML and Line Length Limitations
+
+   HTTP implementations which share code with MHTML [45] implementations
+   need to be aware of MIME line length limitations. Since HTTP does not
+   have this limitation, HTTP does not fold long lines. MHTML messages
+   being transported by HTTP follow all conventions of MHTML, including
+   line length limitations and folding, canonicalization, etc., since
+   HTTP transports all message-bodies as payload (see section 3.7.2) and
+   does not interpret the content or any MIME header lines that might be
+   contained therein.
+
 
-19.6 Additional Features
+19.5 Additional Features
-
-   This appendix documents protocol elements used by some
+   RFC 1945 and RFC 2068 document protocol elements used by some
existing HTTP implementations, but not consistently and correctly across
-   most HTTP/1.1 applications. Implementers should
+   most HTTP/1.1 applications. Implementors are advised to
be aware of these features, but cannot rely upon their presence in, or
interoperability with, other HTTP/1.1 applications. Some of these describe
proposed experimental features, and some describe features that
experimental deployment found lacking that are now addressed in
the base HTTP/1.1 specification.
+
+   A number of other headers, such as Content-Disposition and Title,
+   from SMTP and MIME are also often implemented (see RFC 2076 [37]).
+
+19.5.1 Content-Disposition
+
+   The Content-Disposition response-header field has been proposed as a
+   means for the origin server to suggest a default filename if the user
+   requests that the content is saved to a file. This usage is derived
+   from the definition of Content-Disposition in RFC 1806 [35].
+
+        content-disposition = "Content-Disposition" ":"
+                              disposition-type *( ";" disposition-parm )
+        disposition-type = "attachment" | disp-extension-token
+        disposition-parm = filename-parm | disp-extension-parm
+        filename-parm = "filename" "=" quoted-string
+        disp-extension-token = token
+        disp-extension-parm = token "=" ( token | quoted-string )
 
+   An example is
 
+        Content-Disposition: attachment; filename="fname.ext"
+
+   The receiving user agent SHOULD NOT respect any directory path
+   information present in the filename-parm parameter, which is the only
+   parameter believed to apply to HTTP implementations at this time. The
+   filename SHOULD be treated as a terminal component only.
+
+   If this header is used in a response with the application/octet-
+   stream content-type, the implied suggestion is that the user agent
+   should not display the response, but directly enter a `save response
+   as...' dialog.
+
+   See section 15.5 for Content-Disposition security issues.
-
-19.6.1 Additional Request Methods
-
-19.6.1.1 PATCH
-
-   The PATCH method is similar to PUT except that the entity contains a
-   list of differences between the original version of the resource
-   identified by the Request-URI and the desired content of the resource
-   after the PATCH action has been applied. The list of differences is
-   in a format defined by the media type of the entity (e.g.,
-   "application/diff") and MUST include sufficient information to allow
-   the server to recreate the changes necessary to convert the original
-   version of the resource to the desired version.
-
-   If the request passes through a cache and the Request-URI identifies
-   a currently cached entity, that entity MUST be removed from the
-   cache.  Responses to this method are not cachable.
-
-   The actual method for determining how the patched resource is placed,
-   and what happens to its predecessor, is defined entirely by the
-   origin server. If the original version of the resource being patched
-   included a Content-Version header field, the request entity MUST
-   include a Derived-From header field corresponding to the value of the
-   original Content-Version header field. Applications are encouraged to
-   use these fields for constructing versioning relationships and
-   resolving version conflicts.
-
-   PATCH requests must obey the message transmission requirements set
-   out in section 8.2.
-
-   Caches that implement PATCH should invalidate cached responses as
-   defined in section 13.10 for PUT.
-
-19.6.1.2 LINK
-
-   The LINK method establishes one or more Link relationships between
-   the existing resource identified by the Request-URI and other
-   existing resources. The difference between LINK and other methods
-
-   allowing links to be established between resources is that the LINK
-   method does not allow any message-body to be sent in the request and
-   does not directly result in the creation of new resources.
-
-   If the request passes through a cache and the Request-URI identifies
-   a currently cached entity, that entity MUST be removed from the
-   cache.  Responses to this method are not cachable.
-
-   Caches that implement LINK should invalidate cached responses as
-   defined in section 13.10 for PUT.
-
-19.6.1.3 UNLINK
-
-   The UNLINK method removes one or more Link relationships from the
-   existing resource identified by the Request-URI. These relationships
-   may have been established using the LINK method or by any other
-   method supporting the Link header. The removal of a link to a
-   resource does not imply that the resource ceases to exist or becomes
-   inaccessible for future references.
-
-   If the request passes through a cache and the Request-URI identifies
-   a currently cached entity, that entity MUST be removed from the
-   cache.  Responses to this method are not cachable.
-
-   Caches that implement UNLINK should invalidate cached responses as
-   defined in section 13.10 for PUT.
-
-19.6.2 Additional Header Field Definitions
-
-19.6.2.1 Alternates
-
-   The Alternates response-header field has been proposed as a means for
-   the origin server to inform the client about other available
-   representations of the requested resource, along with their
-   distinguishing attributes, and thus providing a more reliable means
-   for a user agent to perform subsequent selection of another
-   representation which better fits the desires of its user (described
-   as agent-driven negotiation in section 12).
-
-   The Alternates header field is orthogonal to the Vary header field in
-   that both may coexist in a message without affecting the
-   interpretation of the response or the available representations. It
-   is expected that Alternates will provide a significant improvement
-   over the server-driven negotiation provided by the Vary field for
-   those resources that vary over common dimensions like type and
-   language.
-
-   The Alternates header field will be defined in a future
-   specification.
-
-19.6.2.2 Content-Version
 
-   The Content-Version entity-header field defines the version tag
-   associated with a rendition of an evolving entity. Together with the
-   Derived-From field described in section 19.6.2.3, it allows a group
-   of people to work simultaneously on the creation of a work as an
-   iterative process. The field should be used to allow evolution of a
-   particular work along a single path rather than derived works or
-   renditions in different representations.
 
-          Content-Version = "Content-Version" ":" quoted-string
-
-   Examples of the Content-Version field include:
-
-          Content-Version: "2.1.2"
-          Content-Version: "Fred 19950116-12:26:48"
-          Content-Version: "2.5a4-omega7"
-
-19.6.2.3 Derived-From
-
-   The Derived-From entity-header field can be used to indicate the
-   version tag of the resource from which the enclosed entity was
-   derived before modifications were made by the sender. This field is
-   used to help manage the process of merging successive changes to a
-   resource, particularly when such changes are being made in parallel
-   and from multiple sources.
-
-          Derived-From   = "Derived-From" ":" quoted-string
-
-   An example use of the field is:
-
-          Derived-From: "2.1.1"
-
-   The Derived-From field is required for PUT and PATCH requests if the
-   entity being sent was previously retrieved from the same URI and a
-   Content-Version header was included with the entity when it was last
-   retrieved.
-
-19.6.2.4 Link
-
-   The Link entity-header field provides a means for describing a
-   relationship between two resources, generally between the requested
-   resource and some other resource. An entity MAY include multiple Link
-   values. Links at the metainformation level typically indicate
-   relationships like hierarchical structure and navigation paths. The
-   Link field is semantically equivalent to the <LINK> element in
-   HTML.[5]
-
-          Link           = "Link" ":" #("<" URI ">" *( ";" link-param )
-
-          link-param     = ( ( "rel" "=" relationship )
-                             | ( "rev" "=" relationship )
-                             | ( "title" "=" quoted-string )
-                             | ( "anchor" "=" <"> URI <"> )
-                             | ( link-extension ) )
-
-          link-extension = token [ "=" ( token | quoted-string ) ]
-
-          relationship   = sgml-name
-                         | ( <"> sgml-name *( SP sgml-name) <"> )
-
-          sgml-name      = ALPHA *( ALPHA | DIGIT | "." | "-" )
-
-   Relationship values are case-insensitive and MAY be extended within
-   the constraints of the sgml-name syntax. The title parameter MAY be
-   used to label the destination of a link such that it can be used as
-   identification within a human-readable menu. The anchor parameter MAY
-   be used to indicate a source anchor other than the entire current
-   resource, such as a fragment of this resource or a third resource.
-
-   Examples of usage include:
-
-       Link: <http://www.cern.ch/TheBook/chapter2>; rel="Previous"
-
-       Link: <mailto:timbl@w3.org>; rev="Made"; title="Tim Berners-Lee"
-
-   The first example indicates that chapter2 is previous to this
-   resource in a logical navigation path. The second indicates that the
-   person responsible for making the resource available is identified by
-   the given e-mail address.
-
-19.6.2.5 URI
-
-   The URI header field has, in past versions of this specification,
-   been used as a combination of the existing Location, Content-
-   Location, and Vary header fields as well as the future Alternates
-   field (above). Its primary purpose has been to include a list of
-   additional URIs for the resource, including names and mirror
-   locations. However, it has become clear that the combination of many
-   different functions within this single field has been a barrier to
-   consistently and correctly implementing any of those functions.
-   Furthermore, we believe that the identification of names and mirror
-   locations would be better performed via the Link header field. The
-   URI header field is therefore deprecated in favor of those other
-   fields.
-
-          URI-header    = "URI" ":" 1#( "<" URI ">" )
-
-19.7 Compatibility with Previous Versions
+19.6 Compatibility with Previous Versions

It is beyond the scope of a protocol specification to mandate
compliance with previous versions. HTTP/1.1 was deliberately
designed, however, to make supporting previous versions easy. It is
-   worth noting that at the time of composing this specification,
+   worth noting that, at the time of composing this specification (1996),
we would expect commercial HTTP/1.1 servers to:

-  o  
+   -
recognize the format of the Request-Line for HTTP/0.9, 1.0, and 1.1
-  o
+   -
understand any valid request in the format of HTTP/0.9, 1.0, or 1.1;
-  o  respond appropriately with a message in the same major version
+   - respond appropriately with a message in the same major version
used by the client.

And we would expect HTTP/1.1 clients to:

-  o  recognize the format of the Status-Line for HTTP/1.0 and 1.1
+   - recognize the format of the Status-Line for HTTP/1.0 and 1.1
responses;
-  o
+   -
understand any valid response in the format of HTTP/0.9, 1.0, or 1.1.

For most implementations of HTTP/1.0, each connection is established
by the client prior to the request and closed by the server after
-   sending the response. A few implementations implement the Keep-Alive
+   sending the response. Some implementations implement the Keep-Alive
-   version of persistent connections described in section 19.7.1.1.
+   version of persistent connections described in section 19.7.1 of RFC 2068 [33].
-
-19.5 Changes from HTTP/1.0
+19.6.1 Changes from HTTP/1.0
 
    This section summarizes major differences between versions HTTP/1.0
    and HTTP/1.1.
 
-19.5.1 Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses
+19.6.1.1 Changes to Simplify Multi-homed Web Servers and Conserve IP Addresses
 
    The requirements that clients and servers support the Host request-
    header, report an error if the Host request-header (section 14.23) is
@@ -7257,259 +8087,26 @@
    allocated for the sole purpose of allowing special-purpose domain
    names to be used in root-level HTTP URLs. Given the rate of growth of
    the Web, and the number of servers already deployed, it is extremely
    important that all implementations of HTTP (including updates to
    existing HTTP/1.0 applications) correctly implement these
    requirements:
 
-     o  Both clients and servers MUST support the Host request-header.
+      - Both clients and servers MUST support the Host request-header.
 
-     o  Host request-headers are required in HTTP/1.1 requests.
+      - A client that sends an HTTP/1.1 request MUST send a Host header.
 
-     o  Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
+      - Servers MUST report a 400 (Bad Request) error if an HTTP/1.1
         request does not include a Host request-header.
 
-     o  Servers MUST accept absolute URIs.
+      - Servers MUST accept absolute URIs.
-
-19.7.1 Compatibility with HTTP/1.0 Persistent Connections
+19.6.2 Compatibility with HTTP/1.0 Persistent Connections
-
-   Some clients and servers may wish to be compatible with some previous
+   Some clients and servers might wish to be compatible with some previous
implementations of persistent connections in HTTP/1.0 clients and
-   servers. Persistent connections in HTTP/1.0 must be explicitly
+   servers. Persistent connections in HTTP/1.0 are explicitly
negotiated as they are not the default behavior. HTTP/1.0
    experimental implementations of persistent connections are faulty,
    and the new facilities in HTTP/1.1 are designed to rectify these
    problems. The problem was that some existing 1.0 clients may be
@@ -7526,44 +8123,168 @@
    is desired, which is safe to use even when talking to an old proxy
    that ignores Connection. Persistent connections are the default for
    HTTP/1.1 messages; we introduce a new keyword (Connection: close) for
declaring non-persistence.
+   See section 14.10.
-
+   The original HTTP/1.0 form of persistent connections (the Connection:
+   Keep-Alive and Keep-Alive header) is documented in RFC 2068. [33]

-   The following describes the original HTTP/1.0 form of persistent
-   connections.
-
-   When it connects to an origin server, an HTTP client MAY send the
-   Keep-Alive connection-token in addition to the Persist connection-
-   token:
-
-          Connection: Keep-Alive
-
-   An HTTP/1.0 server would then respond with the Keep-Alive connection
-   token and the client may proceed with an HTTP/1.0 (or Keep-Alive)
-   persistent connection.
-
-   An HTTP/1.1 server may also establish persistent connections with
-   HTTP/1.0 clients upon receipt of a Keep-Alive connection token.
-   However, a persistent connection with an HTTP/1.0 client cannot make
-   use of the chunked transfer-coding, and therefore MUST use a
-   Content-Length for marking the ending boundary of each message.
-
-   A client MUST NOT send the Keep-Alive connection token to a proxy
-   server as HTTP/1.0 proxy servers do not obey the rules of HTTP/1.1
-   for parsing the Connection header field.
 
-19.7.1.1 The Keep-Alive Header
 
-   When the Keep-Alive connection-token has been transmitted with a
-   request or a response, a Keep-Alive header field MAY also be
-   included. The Keep-Alive header field takes the following form:
 
-          Keep-Alive-header = "Keep-Alive" ":" 0# keepalive-param
 
-          keepalive-param = param-name "=" value
 
-   The Keep-Alive header itself is optional, and is used only if a
-   parameter is being sent. HTTP/1.1 does not define any parameters.
 
-   If the Keep-Alive header is sent, the corresponding connection token
-   MUST be transmitted. The Keep-Alive header MUST be ignored if
-   received without the connection token.

+19.6.3 Changes from RFC 2068

+   This specification has been carefully audited to correct and
+   disambiguate key word usage; RFC 2068 had many problems in respect to
+   the conventions laid out in RFC 2119 [34].
+
+   Clarified which error code should be used for inbound server failures
+   (e.g. DNS failures). (Section 10.5.5).
+
+   CREATE had a race that required an Etag be sent when a resource is
+   first created. (Section 10.2.2).
+
+   Content-Base was deleted from the specification: it was not
+   implemented widely, and there is no simple, safe way to introduce it
+   without a robust extension mechanism. In addition, it is used in a
+   similar, but not identical fashion in MHTML [45].
+
+   Transfer-coding and message lengths all interact in ways that
+   required fixing exactly when chunked encoding is used (to allow for
+   transfer encoding that may not be self delimiting); it was important
+   to straighten out exactly how message lengths are computed. (Sections
+   3.6, 4.4, 7.2.2, 13.5.2, 14.13, 14.16)
+
+   A content-coding of "identity" was introduced, to solve problems
+   discovered in caching. (section 3.5)
+
+   Quality Values of zero should indicate that "I don't want something"
+   to allow clients to refuse a representation. (Section 3.9)
+
+   The use and interpretation of HTTP version numbers has been clarified
+   by RFC 2145. Require proxies to upgrade requests to highest protocol
+   version they support to deal with problems discovered in HTTP/1.0
+   implementations (Section 3.1)
+
+   Charset wildcarding is introduced to avoid explosion of character set
+   names in accept headers. (Section 14.2)
+
+   A case was missed in the Cache-Control model of HTTP/1.1; s-maxage
+   was introduced to add this missing case. (Sections 13.4, 14.8, 14.9,
+   14.9.3)
+
+   The Cache-Control: max-age directive was not properly defined for
+   responses. (Section 14.9.3)
+
+   There are situations where a server (especially a proxy) does not
+   know the full length of a response but is capable of serving a
+   byterange request. We therefore need a mechanism to allow byteranges
+   with a content-range not indicating the full length of the message.
+   (Section 14.16)
+
+   Range request responses would become very verbose if all meta-data
+   were always returned; by allowing the server to only send needed
+   headers in a 206 response, this problem can be avoided. (Section
+   10.2.7, 13.5.3, and 14.27)
+
+   Fix problem with unsatisfiable range requests; there are two cases:
+   syntactic problems, and range doesn't exist in the document. The 416
+   status code was needed to resolve this ambiguity needed to indicate
+   an error for a byte range request that falls outside of the actual
+   contents of a document. (Section 10.4.17, 14.16)
+
+   Rewrite of message transmission requirements to make it much harder
+   for implementors to get it wrong, as the consequences of errors here
+   can have significant impact on the Internet, and to deal with the
+   following problems:
+
+      1. Changing "HTTP/1.1 or later" to "HTTP/1.1", in contexts where
+         this was incorrectly placing a requirement on the behavior of
+         an implementation of a future version of HTTP/1.x
+
+      2. Made it clear that user-agents should retry requests, not
+         "clients" in general.
+
+      3. Converted requirements for clients to ignore unexpected 100
+         (Continue) responses, and for proxies to forward 100 responses,
+         into a general requirement for 1xx responses.
+
+      4. Modified some TCP-specific language, to make it clearer that
+         non-TCP transports are possible for HTTP.
+
+      5. Require that the origin server MUST NOT wait for the request
+         body before it sends a required 100 (Continue) response.
+
+      6. Allow, rather than require, a server to omit 100 (Continue) if
+         it has already seen some of the request body.
+
+      7. Allow servers to defend against denial-of-service attacks and
+         broken clients.
+
+   This change adds the Expect header and 417 status code. The message
+   transmission requirements fixes are in sections 8.2, 10.4.18,
+   8.1.2.2, 13.11, and 14.20.
+
+   Proxies should be able to add Content-Length when appropriate.
+   (Section 13.5.2)
+
+   Clean up confusion between 403 and 404 responses. (Section 10.4.4,
+   10.4.5, and 10.4.11)
+
+   Warnings could be cached incorrectly, or not updated appropriately.
+   (Section 13.1.2, 13.2.4, 13.5.2, 13.5.3, 14.9.3, and 14.46) Warning
+   also needed to be a general header, as PUT or other methods may have
+   need for it in requests.
+
+   Transfer-coding had significant problems, particularly with
+   interactions with chunked encoding. The solution is that transfer-
+   codings become as full fledged as content-codings. This involves
+   adding an IANA registry for transfer-codings (separate from content
+   codings), a new header field (TE) and enabling trailer headers in the
+   future. Transfer encoding is a major performance benefit, so it was
+   worth fixing [39]. TE also solves another, obscure, downward
+   interoperability problem that could have occurred due to interactions
+   between authentication trailers, chunked encoding and HTTP/1.0
+   clients.(Section 3.6, 3.6.1, and 14.39)
+
+   The PATCH, LINK, UNLINK methods were defined but not commonly
+   implemented in previous versions of this specification. See RFC 2068
+   [33].
+
+   The Alternates, Content-Version, Derived-From, Link, URI, Public and
+   Content-Base header fields were defined in previous versions of this
+   specification, but not commonly implemented. See RFC 2068 [33].
+
+20 Index
+
+   Please see the PostScript version of this RFC for the INDEX.
+
+21.  Full Copyright Statement
+
+   Copyright (C) The Internet Society (1999).  All Rights Reserved.
+
+   This document and translations of it may be copied and furnished to
+   others, and derivative works that comment on or otherwise explain it
+   or assist in its implementation may be prepared, copied, published
+   and distributed, in whole or in part, without restriction of any
+   kind, provided that the above copyright notice and this paragraph are
+   included on all such copies and derivative works.  However, this
+   document itself may not be modified in any way, such as by removing
+   the copyright notice or references to the Internet Society or other
+   Internet organizations, except as needed for the purpose of
+   developing Internet standards in which case the procedures for
+   copyrights defined in the Internet Standards process must be
+   followed, or as required to translate it into languages other than
+   English.
+
+   The limited permissions granted above are perpetual and will not be
+   revoked by the Internet Society or its successors or assigns.
+
+   This document and the information contained herein is provided on an
+   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
+   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
+   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
+   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
+   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+Acknowledgement
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
