.
]PRE]
]INS]
[DEL[
[PRE[
[UNICODE] The Unicode Consortium, "The Unicode Standard -- Version
2.0", Addison-Wesley, 1996.
]PRE]
]DEL]
* 8 Acknowledgements
[DEL[
[PRE[
Chris Newman and Yaron Y. Goland both contributed content to the
security considerations section of this document. In particular,
some text in the security considerations section is copied verbatim
from work in progress, draft-newman-mime-textpara-00, by permission
of the author. Chris Newman additionally contributed content to the
encoding considerations sections. Dan Connolly contributed content
discussing when to use text/xml. Discussions with Ned Freed and Dan
Connolly helped refine the author's understanding of the text media
type; feedback from Larry Masinter was also very helpful in
understanding media type registration issues.
]PRE]
[PRE[
Members of the W3C XML Working Group and XML Special Interest group
have made significant contributions to this document, and the authors
would like to specially recognize James Clark, Martin Duerst, Rick
Jelliffe, Gavin Nicol for their many thoughtful comments.
]PRE]
]DEL]
* 9 Addresses of Authors
[DEL[
[PRE[
E. James Whitehead, Jr.
Dept. of Information and Computer Science
University of California, Irvine
Irvine, CA 92697-3425
]PRE]
[PRE[
EMail: ejw@@ics.uci.edu
]PRE]
[PRE[
Murata Makoto (Family Given)
Fuji Xerox Information Systems,
KSP 9A7, 2-1, Sakado 3-chome, Takatsu-ku,
Kawasaki-shi, Kanagawa-ken,
213 Japan
]PRE]
[PRE[
EMail: murata@@fxis.fujixerox.co.jp
]PRE]
]DEL]
* Authors' Addresses
[INS[
[PRE[
MURATA Makoto (FAMILY Given)
IBM Tokyo Research Laboratory
1623-14, Shimotsuruma
Yamato-shi, Kanagawa-ken 242-8502
Japan
]PRE]
[PRE[
Phone: +81-46-215-4678
EMail: mmurata@@trl.ibm.co.jp
]PRE]
[PRE[
Simon St.Laurent
simonstl.com
1259 Dryden Road
Ithaca, New York 14850
USA
]PRE]
[PRE[
EMail: simonstl@@simonstl.com
URI: http://www.simonstl.com/
]PRE]
[PRE[
Dan Kohn
Skymoon Ventures
3045 Park Boulevard
Palo Alto, California 94306
USA
]PRE]
[PRE[
Phone: +1-650-327-2600
EMail: dan@@dankohn.com
URI: http://www.dankohn.com/
]PRE]
]INS]
* Appendix A. Why Use the '+xml' Suffix for XML-Based MIME Types?
[INS[
[PRE[
Although the use of a suffix was not considered as part of the
original MIME architecture, this choice is considered to provide the
most functionality with the least potential for interoperability
problems or lack of future extensibility. The alternatives to the
'+xml' suffix and the reason for its selection are described below.
]PRE]
A.1 Why not just use text/xml or application/xml and let the XML
[PRE[
processor dispatch to the correct application based on the
referenced DTD?
]PRE]
[PRE[
text/xml and application/xml remain useful in many situations,
especially for document-oriented applications that involve combining
XML with a stylesheet in order to present the data. However, XML is
also used to define entirely new data types, and an XML-based format
such as image/svg+xml fits the definition of a MIME media type
exactly as well as image/png[PNG] does. (Note that image/svg+xml is
not yet registered.) Although extra functionality is available for
MIME processors that are also XML processors, XML-based media types
-- even when treated as opaque, non-XML media types -- are just as
useful as any other media type and should be treated as such.
]PRE]
[PRE[
Since MIME dispatchers work off of the MIME type, use of text/xml or
application/xml to label discrete media types will hinder correct
dispatching and general interoperability. Finally, many XML
documents use neither DTDs nor namespaces, yet are perfectly legal
XML.
]PRE]
A.2 Why not create a new subtree (e.g., image/xml.svg) to represent XML
[PRE[
MIME types?
]PRE]
[PRE[
The subtree under which a media type is registered -- IETF, vendor
(*/vnd.*), or personal (*/prs.*); see [RFC2048] for details -- is
completely orthogonal from whether the media type uses XML syntax or
not. The suffix approach allows XML document types to be identified
within any subtree. The vendor subtree, for example, is likely to
include a large number of XML-based document types. By using a
suffix, rather than setting up a separate subtree, those types may
remain in the same location in the tree of MIME types that they would
have occupied had they not been based on XML.
]PRE]
A.3 Why not create a new top-level MIME type for XML-based media types?
[PRE[
The top-level MIME type (e.g., model/*[RFC2077]) determines what kind
of content the type is, not what syntax it uses. For example, agents
using image/* to signal acceptance of any image format should
certainly be given access to media type image/svg+xml, which is in
]PRE]
[PRE[
all respects a standard image subtype. It just happens to use XML to
describe its syntax. The two aspects of the media type are
completely orthogonal.
]PRE]
[PRE[
XML-based data types will most likely be registered in ALL top-level
categories. Potential, though currently unregistered, examples could
include application/mathml+xml[MathML] and image/svg+xml[SVG].
]PRE]
A.4 Why not just have the MIME processor 'sniff' the content to
[PRE[
determine whether it is XML?
]PRE]
[PRE[
Rather than explicitly labeling XML-based media types, the processor
could look inside each type and see whether or not it is XML. The
processor could also cache a list of XML-based media types.
]PRE]
[PRE[
Although this method might work acceptably for some mail
applications, it would fail completely in many other uses of MIME.
For instance, an XML-based web crawler would have no way of
determining whether a file is XML except to fetch it and check. The
same issue applies in some IMAP4[RFC2060] mail applications, where
the client first fetches the MIME type as part of the message
structure and then decides whether to fetch the MIME entity.
Requiring these fetches just to determine whether the MIME type is
XML could have significant bandwidth and latency disadvantages in
many situations.
]PRE]
[PRE[
Sniffing XML also isn't as simple as it might seem. DOCTYPE
declarations aren't required, and they can appear fairly deep into a
document under certain unpreventable circumstances. (E.g., the XML
declaration, comments, and processing instructions can occupy space
before the DOCTYPE declaration.) Even sniffing the DOCTYPE isn't
completely reliable, thanks to a variety of issues involving default
values for namespaces within external DTDs and overrides inside the
internal DTD. Finally, the variety in potential character encodings
(something XML provides tools to deal with), also makes reliable
sniffing less likely.
]PRE]
A.5 Why not use a MIME parameter to specify that a media type uses XML
[PRE[
syntax?
]PRE]
[PRE[
For example, one could use "Content-Type: application/iotp;
alternate-type=text/xml" or "Content-Type: application/iotp;
syntax=xml".
]PRE]
[PRE[
Section 5 of [RFC2045] says that "Parameters are modifiers of the
media subtype, and as such do not fundamentally affect the nature of
the content". However, all XML-based media types are by their nature
]PRE]
[PRE[
always XML. Parameters, as they have been defined in the MIME
architecture, are never invariant across all instantiations of a
media type.
]PRE]
[PRE[
More practically, very few if any MIME dispatchers and other MIME
agents support dispatching off of a parameter. While MIME agents on
the receiving side will need to be updated in either case to support
(or fall back to) generic XML processing, it has been suggested that
it is easier to implement this functionality when acting off of the
media type rather than a parameter. More important, sending agents
require no update to properly tag an image as "image/svg+xml", but
few if any sending agents currently support always tagging certain
content types with a parameter.
]PRE]
A.6 How about labeling with parameters in the other direction (e.g.,
[PRE[
application/xml; Content-Feature=iotp)?
]PRE]
[PRE[
This proposal fails under the simplest case, of a user with neither
knowledge of XML nor an XML-capable MIME dispatcher. In that case,
the user's MIME dispatcher is likely to dispatch the content to an
XML processing application when the correct default behavior should
be to dispatch the content to the application responsible for the
content type (e.g., an ecommerce engine for
application/iotp+xml[RFC2801], once this media type is registered).
]PRE]
[PRE[
Note that even if the user had already installed the appropriate
application (e.g., the ecommerce engine), and that installation had
updated the MIME registry, many operating system level MIME
registries such as .mailcap in Unix and HKEY_CLASSES_ROOT in Windows
do not currently support dispatching off a parameter, and cannot
easily be upgraded to do so. And, even if the operating system were
upgraded to support this, each MIME dispatcher would also separately
need to be upgraded.
]PRE]
A.7 How about a new superclass MIME parameter that is defined to apply
[PRE[
to all MIME types (e.g., Content-Type: application/iotp;
$superclass=xml)?
]PRE]
[PRE[
This combines the problems of Appendix A.5 and Appendix A.6.
]PRE]
[PRE[
If the sender attaches an image/svg+xml file to a message and
includes the instructions "Please copy the French text on the road
sign", someone with an XML-aware MIME client and an XML browser but
no support for SVG can still probably open the file and copy the
text. By contrast, with superclasses, the sender must add superclass
support to her existing mailer AND the receiver must add superclass
support to his before this transaction can work correctly.
]PRE]
[PRE[
If the receiver comes to rely on the superclass tag being present and
applications are deployed relying on that tag (as always seems to
happen), then only upgraded senders will be able to interoperate with
those receiving applications.
]PRE]
A.8 What about adding a new parameter to the Content-Disposition header
[PRE[
or creating a new Content-Structure header to indicate XML syntax?
]PRE]
[PRE[
This has nearly identical problems to Appendix A.7, in that it
requires both senders and receivers to be upgraded, and few if any
operating systems and MIME dispatchers support working off of
anything other than the MIME type.
]PRE]
A.9 How about a new Alternative-Content-Type header?
[PRE[
This is better than Appendix A.8, in that no extra functionality
needs to be added to a MIME registry to support dispatching of
information other than standard content types. However, it still
requires both sender and receiver to be upgraded, and it will also
fail in many cases (e.g., web hosting to an outsourced server), where
the user can set MIME types (often through implicit mapping to file
extensions), but has no way of adding arbitrary HTTP headers.
]PRE]
A.10 How about using a conneg tag instead (e.g., accept-features:
[PRE[
(syntax=xml))?
]PRE]
[PRE[
When the conneg protocol is fully defined, this may potentially be a
reasonable thing to do. But given the limited current state of
conneg[RFC2703] development, it is not a credible replacement for a
MIME-based solution.
]PRE]
A.11 How about a third-level content-type, such as text/xml/rdf?
[PRE[
MIME explicitly defines two levels of content type, the top-level for
the kind of content and the second-level for the specific media type.
[RFC2048] extends this in an interoperable way by using prefixes to
specify separate trees for IETF, vendor, and personal registrations.
This specification also extends the two-level type by using the '
+xml' suffix. In both cases, processors that are unaware of these
later specifications treat them as opaque and continue to
interoperate. By contrast, adding a third-level type would break the
current MIME architecture and cause numerous interoperability
failures.
]PRE]
A.12 Why use the plus ('+') character for the suffix '+xml'?
[PRE[
As specified in Section 5.1 of [RFC2045], a tspecial can't be used:
]PRE]
[PRE[
tspecials :=
"(" / ")" / "<" / ">" / "@@" /
"," / ";" / ":" / "\" / <">
"/" / "[" / "]" / "?" / "="
]PRE]
[PRE[
It was thought that "." would not be a good choice since it is
already used as an additional hierarchy delimiter. Also, "*" has a
common wildcard meaning, and "-" and "_" are common word separators
and easily confused. The characters %'`#& are frequently used for
quoting or comments and so are not ideal.
]PRE]
[PRE[
That leaves: ~!$^+{}|
]PRE]
[PRE[
Note that "-" is used heavily in the current registry. "$" and "_"
are used once each. The others are currently unused.
]PRE]
[PRE[
It was thought that '+' expressed the semantics that a MIME type can
be treated (for example) as both scalable vector graphics AND ALSO as
XML; it is both simultaneously.
]PRE]
A.13 What is the semantic difference between application/foo and
[PRE[
application/foo+xml?
]PRE]
[PRE[
MIME processors that are unaware of XML will treat the '+xml' suffix
as completely opaque, so it is essential that no extra semantics be
assigned to its presence. Therefore, application/foo and
application/foo+xml SHOULD be treated as completely independent media
types. Although, for example, text/calendar+xml could be an XML
version of text/calendar[RFC2445], it is possible that this
(hypothetical) new media type would include new semantics as well as
new syntax, and in any case, there would be many applications that
support text/calendar but had not yet been upgraded to support
text/calendar+xml.
]PRE]
A.14 What happens when an even better markup language (e.g., EBML) is
[PRE[
defined, or a new category of data?
]PRE]
[PRE[
In the ten years that MIME has existed, XML is the first generic data
format that has seemed to justify special treatment, so it is hoped
that no further suffixes will be necessary. However, if some are
later defined, and these documents were also XML, they would need to
specify that the '+xml' suffix is always the outermost suffix (e.g.,
application/foo+ebml+xml not application/foo+xml+ebml). If they were
not XML, then they would use a regular suffix (e.g.,
application/foo+ebml).
]PRE]
A.15 Why must I use the '+xml' suffix for my new XML-based media type?
[PRE[
You don't have to, but unless you have a good reason to explicitly
disallow generic XML processing, you should use the suffix so as not
to curtail the options of future users and developers.
]PRE]
[PRE[
Whether the inventors of a media type, today, design it for dispatch
to generic XML processing machinery (and most won't) is not the
critical issue. The core notion is that the knowledge that some
media type happens to use XML syntax opens the door to unanticipated
kinds of processing beyond those envisioned by its inventors, and on
this basis identifying such encoding is a good and useful thing.
]PRE]
[PRE[
Developers of new media types are often tightly focused on a
particular type of processing that meets current needs. But there is
no need to rule out generic processing as well, which could make your
media type more valuable over time. It is believed that registering
with the '+xml' suffix will cause no interoperability problems
whatsoever, while it may enable significant new functionality and
interoperability now and in the future. So, the conservative
approach is to include the '+xml' suffix.
]PRE]
]INS]
** Appendix B. Changes from RFC 2376
[PRE[
There are numerous and significant differences between this
specification and [RFC2376], which it obsoletes. This appendix
summarizes the major differences only.
]PRE]
[PRE[
First, text/xml-external-parsed-entity and application/xml-external-
parsed-entity are added as media types for external parsed entities,
and text/xml and application/xml are now prohibited.
]PRE]
[PRE[
Second, application/xml-dtd is added as a media type for external DTD
subsets and external parameter entities, and text/xml and
application/xml are now prohibited.
]PRE]
[PRE[
Third, "utf-16le" and "utf-16be" are added. RFC 2781 has introduced
these BOM-less variations of the UTF-16 family.
]PRE]
[PRE[
Fourth, a naming convention ('+xml') for XML-based media types has
been added, which also updates [RFC2048] as described in Section 7.
By following this convention, an XML-based media type can be easily
recognized as such.
]PRE]
* Appendix C. Acknowledgements
[INS[
[PRE[
This document reflects the input of numerous participants to the
ietf-xml-mime@@imc.org mailing list, though any errors are the
responsibility of the authors. Special thanks to:
]PRE]
[PRE[
Mark Baker, James Clark, Dan Connolly, Martin Duerst, Ned Freed,
Yaron Goland, Rick Jelliffe, Larry Masinter, David Megginson, Keith
Moore, Chris Newman, Gavin Nicol, Marshall Rose, Jim Whitehead and
participants of the XML activity at the W3C.
]PRE]
]INS]
* [DEL[10]] Full Copyright Statement
[PRE[
Copyright (C) The Internet Society ([DEL[1998]] [INS[2001]]). All Rights Reserved.
]PRE]
[PRE[
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.
]PRE]
[PRE[
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
]PRE]
[PRE[
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.
]PRE]
[INS[
]INS]
** Acknowledgement
[PRE[
Funding for the RFC Editor function is currently provided by the
Internet Society.
]PRE]
* License
[[RFCのライセンス]]
* メモ
- [[..//]] 参照。
[2]
([[babarasprava]] [ahtung@mail.com])
[3]
nice site
http://dentistry.ho.com.ua/
http://dentistry.ho.com.ua/
http://dentistry.ho.com.ua/
http://dentistry.ho.com.ua/
http://dentistry.ho.com.ua/cosmetic-dentistry.html
cosmetic dentistry USA
http://dentistry.ho.com.ua/cosmetic-dentistry.html
cosmetic dentistry USA
http://dentistry.ho.com.ua/
http://dentistry.ho.com.ua/
nice site
http://air-fare.teach-nology.com
Air Fare Cheap
Air Fares, Cheap Air Fares Uk, Cheap CHEAP AIR FARE http://air-fare.teach-nology.com Cheap Air Fare - Cheap Domestic Air Fares, Cheap Air Fares Uk
Best airfare consolidators, cheep airfare, european airfare, cancun airfare. http://air-fare.teach-nology.com/airfare.html discounted airfare, airfare
discounted airfare, airfare