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1
2 INTERNET DRAFT
3
4 Hypertext links in HTML
5 draft-ietf-html-relrev-00.txt
6
7 today
8
9 Murray Maloney Liam Quin
10 SoftQuad Inc. SoftQuad Inc.
11 murray@sq.com lee@sq.com
12
13 Status of this Memo
14 This document is an Internet Draft. Internet Drafts are
15 working documents of the Internet Engineering Task Force
16 (IETF), its Areas, and its Working Groups. Note that other
17 groups may also distribute working documents as Internet
18 Drafts.
19
20 Internet Drafts are draft documents valid for a maximum of six
21 months. Internet Drafts may be updated, replaced, or
22 obsoleted by other documents at any time. It is not
23 appropriate to use Internet Drafts as reference material or to
24 cite them other than as a ``working draft'' or ``work in
25 progress.'' Please check the 1id-abstracts.txt listing
26 contained in the internet-drafts Shadow Directories on
27 nic.ddn.mil, venera.isi.edu, nnsc.nsf.net, nic.nordu.net,
28 ftp.nisc.sri.com, or munnari.oz.au to learn the current status
29 of any Internet Draft.
30
31 This is a working document only, it should neither be cited
32 nor quoted in any formal document.
33
34 This document will expire before 7 June 1996.
35
36 Distribution of this document is unlimited.
37
38 Please send comments to the author(s).
39
40 Table of Contents
41 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
42 2. Anchors and Targets . . . . . . . . . . . . . . . . . . . . . 3
43 2a. Anchors . . . . . . . . . . . . . . . . . . . . . . . . . 3
44 2b. Targets . . . . . . . . . . . . . . . . . . . . . . . . . 4
45 3. The LINK and A Elements and Their Attributes . . . . . . . . 5
46 3a. The LINK Element . . . . . . . . . . . . . . . . . . . . . 5
47 3b. The A Element . . . . . . . . . . . . . . . . . . . . . . 6
48 3c. Common Attributes . . . . . . . . . . . . . . . . . . . . 6
49 4. The REL and REV Attribute Values . . . . . . . . . . . . . . . 8
50 4a. Legacy . . . . . . . . . . . . . . . . . . . . . . . . . . 8
51 4b. Browser-defined Links . . . . . . . . . . . . . . . . . . 9
52 4c. Navigational Node Links . . . . . . . . . . . . . . . . . 9
53 4d. Hierarchy Links . . . . . . . . . . . . . . . . . . . . . 10
54 4e. Sequence Links . . . . . . . . . . . . . . . . . . . . . . 11
55 4f. Related Documents . . . . . . . . . . . . . . . . . . . . 12
56 4g. Meta Documents . . . . . . . . . . . . . . . . . . . . . . 14
57 4f. Other REL and REV Values Under Discussion . . . . . . . . 16
58 5. Hypertext Includes . . . . . . . . . . . . . . . . . . . . . 18
59 Murray & Quin [Page 1]
60
61 INTERNET DRAFT Hypertext Links in HTML December 1995
62 5a. INCLUDE as a REL or REV Value . . . . . . . . . . . . . . 18
63 5b. INCLUDE as an Element . . . . . . . . . . . . . . . . . . 19
64 5c. SGML external entitities . . . . . . . . . . . . . . . . . 19
65 6. Hypertext Paths . . . . . . . . . . . . . . . . . . . . . . . 19
66 7. Proposed New Attributes for A and LINK Elements . . . . . . . 20
67 7a. ACTION or STYLE or PROCESS or PRESENT . . . . . . . . . . 20
68 7b. TARGET . . . . . . . . . . . . . . . . . . . . . . . . . . 21
69 7c. DINGBAT . . . . . . . . . . . . . . . . . . . . . . . . . 21
70 7d. HILITE or HIGHLIGHT . . . . . . . . . . . . . . . . . . . 21
71 7e. METHOD . . . . . . . . . . . . . . . . . . . . . . . . . . 22
72 7f. SRC . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
73 7g. WHEN . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
74 7h. OBSOLETES, UPDATES and DERIVED-FROM: . . . . . . . . . . . 23
75 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
76
77 Hypertext links in HTML
78
79 This is a discussion paper: It was initiated through discussion on the
80 HTML Working Group mailing list.
81
82 Hypertext link relationships, specified by using the REL and REV
83 attributes of the LINK and A elements, were conceived of as an early
84 feature of the HTML language. Amidst all of the various and sundry
85 efforts that have been undertaken to advance HTML and the World Wide
86 Web, the definition of a small set of widely accepted hypertext
87 relationships has yet to be agreed upon and deployed in user agents.
88
89 Hypertext link relationships, and the attendant REL and REV attributes
90 of the LINK and A elements, are discussed in Dave Raggett's Internet
91 Draft on HTML 3.0. In addition, The Santa Cruz Operation, Inc (SCO) has
92 developed an HTML user agent, based on Mosaic, which incorporates the
93 use of the REL attribute of the LINK element.
94
95 The first draft of this paper was based on Dave Raggett's paper and on
96 the author's experience with a partial implementation at SCO. Others
97 have contributed to the development of this paper through discussions on
98 the html-wg mailing list and through private correspondence with the
99 author. (See the Acknowledgements section.)
100
101 1. Introduction
102 The hypertext link mechanism is the connective tissue used to weave
103 the World Wide Web. A hypertext link is an object which specifies
104 a connection between any arbitrary addressable objects, locations,
105 or resources.
106
107 A hypertext link typically consists of an anchor and a target, each
108 of which may be further classified and between which relationships
109 may be identified. In HTML, there are several language elements
110 which are used to identify anchors and targets and thus support the
111 hypertext link mechanism.
112
113 The anchor of a hypertext link is typically presented to the user,
114 through an HTML user agent, as a highlighted object (a word, phrase,
115 graphic image, etc.). Not all anchors of hypertext links must be
116 represented as highlighted within the document or the application.
117 An HTML user agent may, as appropriate, act upon a hypertext link by
118 taking immediate action, such as presenting a concurrent window. A
119 user agent may, in some cases, simply ignore an anchor and its
120 Murray & Quin [Page 2]
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122 INTERNET DRAFT Hypertext Links in HTML December 1995
123 hypertext link.
124
125 An HTML user agent is free to provide whatever mechanism it chooses
126 to allow the user to traverse from anchor to target. Typically,
127 graphical applications provide for user interaction via a pointing
128 device such as a mouse. Typically, non-graphical text-based
129 applications provide for user interaction via keyboard and arrow
130 selection.
131
132 Different hypertext links may have different behavior associated
133 with them. For example, a link to a Table of Contents may be
134 presented as an icon, with an appropriate label, in a tool bar.
135 Another application may present the same link as a simultaneous view
136 of the document in an alternate window or a concurrent pane. A
137 hypertext link may also initiate a software program, or present
138 audio, graphics, video, print, speech synthesis or braille.
139
140 HTML provides a mechanism for specifying the relationship between an
141 anchor and a target as seen from either end of the hypertext link.
142 The LINK and the A elements each provide a REL and a REV attribute
143 which may be set with values to identify these relationships. The
144 IMG element and the SRC attribute can also be used to form links.
145
146 This purpose of this document is to discuss and formalize hypertext
147 anchors as currently implemented on the World Wide Web, and to
148 propose REL/REV relationships that are useful and consistent with
149 current usage. This paper is intended to describe hypertext links,
150 anchors and targets, classes and relationships. It is also intended
151 to provide suggestions or hints for authors and publishers, and for
152 developers of HTML user agents to guide them in using the hypertext
153 link mechanism effectively.
154
155 NOTE: This document does not address issues associated with
156 non-practiced usages of hypertext anchors, in particular the
157 inclusion/embedding of program applications (e.g. Java applets),
158 within HTML documents.
159
160 2. Anchors and Targets
161 2a. Anchors
162 An anchor is any object which acts as a hypertext link to a
163 target. An anchor may be a highlighted phrase within an HTML
164 document, an icon on an HTML user-agent tool-bar or menu item, an
165 active graphic, or an image map. An anchor may also be an object
166 which is included by reference, such a graphic image.
167
168 There are four ways to specify an anchor in HTML:
169 * the A element
170 * the LINK element
171 * the SRC attribute as used on
172 * the IMG element
173 * the UL element (HTML 3.0 proposal)
174 * the LI element (HTML 3.0 proposal)
175 * the NOTE element (HTML 3.0 proposal)
176 * the ISMAP attribute as used on the IMG element
177
178 An anchor is typically specified using the A element. This form
179 of anchor is used to highlight an object (word, phrase, graphic
180 image, etc.) which may be activated by a user to traverse the
181 Murray & Quin [Page 3]
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183 INTERNET DRAFT Hypertext Links in HTML December 1995
184 link by using the following form:
185 <A HREF="target">object to highlight</A>
186
187 An anchor may also be specified using the LINK element. This form
188 of anchor is used to establish a hypertext link between an entire
189 HTML document and another addressable object or resource. A LINK
190 element is considered document meta-information (it does not mark
191 a link relationship specific to any part of the body), and is
192 therefore restricted to lie within the document HEAD. Because
193 the LINK element is only allowed within the HEAD of an HTML
194 document, and because it has no content, it is not usually
195 represented within the body of an HTML document as seen through a
196 user agent. Its purpose is solely to inform the user agent that a
197 link exists. The user agent may process or ignore these links as
198 it sees fit, but it may, for example, present an icon on a
199 toolbar for the user to traverse the link. An example of LINK
200 usage is:
201 <LINK HREF="chapter1.html" REL=PREVIOUS>
202 <LINK HREF="chapter3.html" REL=NEXT>
203
204 An anchor may also be specified using the IMG element. This form
205 of anchor is used to establish a hypertext link to include a
206 graphic image. Its purpose it solely to inform the user agent
207 that a graphic image may be placed at the current location if the
208 user agent is capable of doing so, and if the user has enabled
209 viewing of graphic images. An example of this form of IMG usage
210 is:
211 <IMG SRC="image.gif">
212
213 An anchor may also be specified by providing a value to the SRC
214 attribute on any HTML element which supports that attribute.
215 For example:
216 <NOTE CLASS=WARNING SRC=WARNING.gif> ... </NOTE>
217
218 A specialized active hypertext link anchor known as an image map
219 may be specified by using the IMG element in combination with the
220 SRC and ISMAP attributes. An example of this form of IMG usage
221 is:
222 <A HREF="..."><IMG SRC="image.gif" ISMAP></A>
223
224 2b. Targets
225 A target is any addressable object or resource which typically
226 serves as the destination of a hypertext link. The destination
227 may be another HTML document, a fragment within the same or
228 another HTML document, or any other type of object or resource.
229
230 A target may also be an aggregate link which can be presented as
231 a list of possible targets from which a user can select. A Table
232 of Contents may be an example of an aggregate link. The result of
233 a query is an other example.
234
235 Any addressable object may serve as the target of a hypertext
236 link. Typically, a target is addressed by specifying a URL/URI as
237 the value of an HREF or SRC attribute on HTML elements which
238 support those attributes.
239
240 HTML also provides a number of language elements which may be
241 used to identify a target within an HTML document and to specify
242 Murray & Quin [Page 4]
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244 INTERNET DRAFT Hypertext Links in HTML December 1995
245 the base location from which relative addresses should be
246 formed.
247
248 There are four ways to specify a target within an HTML document:
249 * the BASE element
250 * the NAME attribute of the A element
251 * the ID attribute of various elements, including A and LINK
252 (HTML 3.0 proposal)
253 * the NAME attribute of the LINK element
254
255 The base location of a document may be recorded in the BASE
256 element in the HEAD of the document. The base location is the
257 address from which all relative URL addresses are to be formed.
258 For example:
259 <BASE HREF="http://server.domain/whatever">
260
261 A target may be specified by surrounding any object (word,
262 phrase, graphic image, etc.) with an A element having a non-null
263 NAME attribute, and the target is considered to be the beginning
264 of the encapsulated object. For example:
265 <A NAME="nametoken">target object</A>
266
267 A target may also be specified by providing a value for the ID
268 attribute on any HTML element which supports that attribute.
269 For example:
270 <P ID="PARA-1.1">
271
272 A target may also be specified as an attribute to a LINK element.
273 A LINK element may only be used within the head of an HTML
274 document, and it has no content. For example:
275 <HTML>
276 <HEAD>
277 <LINK NAME="THIS">
278 <LINK NAME="THAT" HREF="THAT.html">
279 </HEAD>
280
281 3. The LINK and A Elements and Their Attributes
282 The LINK and A elements share a set of common attributes. Except
283 where noted, the semantics of those attributes is the same.
284
285 3a. The LINK Element
286 The LINK element indicates a hypertext link relationship between
287 the document in which it is found and some other object. Any
288 number of LINK elements may be used within the head of an HTML
289 document. The LINK element is empty (does not have a closing
290 tag). The LINK element takes the same attributes as the A
291 (anchor) element.
292
293 The hypertext link described by the LINK element is not typically
294 represented within the text area of an HTML user agent. Instead,
295 an HTML user agent is free to either ignore any LINK element and
296 the hypertext link associated with it, or to represent the
297 hypertext link in some other way.
298
299 Presenting hypertext links as active icons in a toolbar is one
300 way to present them to the user. Another may be to present the
301 target document in a concurrent window, such as with a table of
302 contents.
303 Murray & Quin [Page 5]
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305 INTERNET DRAFT Hypertext Links in HTML December 1995
306
307 3b. The A Element
308 The A element is used to indicate the start (anchor) or end
309 (target) of a hypertext link within the body of an HTML
310 document.
311
312 The hypertext link described by the A element is typically
313 represented as a highlighted object (word, phrase, graphical
314 image, etc.) within the text area of an HTML user agent.
315
316 3c. Common Attributes
317 For the purposes of this discussion, the following is a list with
318 descriptions of the most important common attributes. All of the
319 attributes listed here are part of HTML 2.0 except for CLASS, ID
320 and MD, which are discussed in Dave Raggett's Internet Draft on
321 HTML 3.0.
322
323 CLASS
324 The CLASS attribute value is used to subclass the hypertext
325 link. The CLASS attribute is most often used as a generalized
326 identifier to which style information may be attached by a
327 stylesheet mechanism.
328
329 The CLASS attribute may also be used to subclass LINK
330 elements, thereby differentiating hypertext links with common
331 REL or REV values. This may provide unambiguous syntax, for
332 example, for multiple LINK elements with REL=NEXT within a
333 document. Thus, alternate paths through a document can be
334 coded within the document. For example:
335 <LINK REL=NEXT CLASS=NOVICE HREF=... >
336 <LINK REL=NEXT CLASS=VETERAN HREF=... >
337 <LINK REL=NEXT CLASS=EXPERT HREF=... >
338 <LINK REL=NEXT CLASS=GURU HREF=... >
339
340 Multiple CLASS values may be specified. The potential list of
341 CLASS attribute values is open-ended. However, practical
342 application will likely require definition and specification
343 of at least a small set of accepted keywords, and agreement
344 on processing expectations for arbitrary keywords. The
345 keywords used in the previous example are typical of the
346 type of keywords which may be specified, but are not
347 proposed.
348
349 HREF
350 The HREF attribute value specifies the location of a
351 destination or resource, expressed in the Universal Resource
352 Identifier (URI) notation. Only one HREF value may be
353 specified. An HTML user agent may present the value of the
354 HREF attribute in an information area when the user positions
355 the mouse over the anchor or otherwise indicates interest in
356 the anchor.
357
358 ID
359 The ID attribute specifies an SGML identifier used as the
360 target of hypertext links or for naming particular elements
361 in associated style sheets. Only one ID value may be
362 specified. The attribute value must be unique within the
363 document.
364 Murray & Quin [Page 6]
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366 INTERNET DRAFT Hypertext Links in HTML December 1995
367
368 MD
369 The MD attribute specifies a message digest or cryptographic
370 checksum for the target of the hypertext link. This attribute
371 is used by a user agent to verify that the linked object is
372 the same one that the author intended.
373
374 NAME
375 The NAME attribute specifies a named location within an HTML
376 document and is used in forming addresses to target specific
377 locations within an HTML document. Only one NAME value may be
378 specified. The attribute value must be unique within the
379 document.
380
381 REL
382 The REL attribute specifies the relationship of the target to
383 the anchor. For example, REL=NEXT is used to indicate that
384 the target is the next logical document in an author-
385 specified sequence. The REL attribute can also be used to
386 support search for links serving particular relationships.
387
388 Multiple REL values may be specified. Aggregate links can be
389 formed by including multiple LINK elements with equivalent
390 REL values. Activating the link, in that case, may lead to a
391 virtual menu from which the user can make a selection.
392
393 The nature of a link relationship is not always obvious from
394 the attribute value. Section 4 (Meaning of REL and REV
395 Attribute Values) describes commonly accepted values.
396 Designers of HTML user agents can use these descriptions as a
397 guide to implementation of browser or agent behavior.
398
399 REV
400 The REV attribute specifies the relationship of the anchor to
401 the target. For example, REV=TOP is used to indicate that the
402 anchor is the top of an author-specified hierarchical tree
403 of which the target is a branch or node.
404
405 Multiple REV values may be specified. A Table of Contents may
406 contain a series of anchors which specify REV=TOC.
407
408 The nature of a link relationship is not always obvious from
409 the attribute value. Section 4 (Meaning of REL and REV
410 Attribute Values) describes commonly accepted values.
411 Designers of HTML user agents can use these descriptions as a
412 guide to implementation of browser or agent behavior.
413
414 TITLE
415 The TITLE attribute is typically used to describe the linked
416 object specified by the HREF attribute. The attribute value
417 is a character string which may include spaces and
418 punctuation. An HTML user agent may present the value of the
419 TITLE attribute in an information area when the user
420 positions the mouse over the anchor or otherwise indicates
421 interest in the anchor. Authors/publishers can thereby
422 provide greater context to the user to aid them in making
423 decisions about whether to traverse a hypertext link.
424
425 Murray & Quin [Page 7]
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427 INTERNET DRAFT Hypertext Links in HTML December 1995
428 An HTML user agent may also use the value of the TITLE
429 attribute to set the value of an email subject field when the
430 HREF value uses the `mailto:' scheme. In this way, the
431 subject field may be preset with value that the author's mail
432 agent can recognize and process.
433
434 Although the HREF and TITLE attributes have been singled out in
435 the list above, any of these attribute values may be presented in
436 an information area when the user positions the mouse over the
437 anchor or otherwise indicates interest in the anchor. For
438 example, an HTML user agent which is also an HTML editor may
439 display the value of ID or NAME attributes.
440
441 4. The REL and REV Attribute Values
442
443 The potential list of valid values for REL and REV is open-ended,
444 and this document is not intended to preclude the use or adoption of
445 other or additional values. In fact, it is anticipated that
446 hypertext applications which support specific knowledge domains will
447 need to develop specialized sets of keywords. It is hoped that the
448 development of extensions will not occur in isolation, and that
449 coordination of extensions among various interested parties will
450 prevent namespace contention or collision.
451
452 Further, HTML user agents should continue to be liberal in accepting
453 new or alternate values, inasmuch as any name token is a legal
454 value. The HTML specification declares that REL/REV values are SGML
455 name tokens. That is, within the previously described syntactical
456 constraints, a REL or REV relationship value may be any arbitrary,
457 author-defined value that the author or publisher considers
458 important. In some cases, the HTML user agent may choose to present
459 relationships that it recognizes in a richer style, while
460 continuing to present unfamiliar ones in the default style.
461
462 The REL and REV attributes are defined as NAMES in the SGML DTD for
463 the HyperText Markup Language (HTML). As such, the legal values
464 which may be assigned to the REL or REV attribute are zero or more
465 name tokens. Name tokens are case-insensitive, must begin with an
466 alpha character, may include digits (0-9), period or hyphen, and may
467 be separated by spaces. The name tokens listed and described in this
468 section are being recommended as commonly accepted relationships
469 between and among objects in a hypertext collection.
470
471 When a single name token is specified as a REL or REV attribute,
472 double quotes surrounding the attribute value are optional. When
473 multiple name tokens are specified, double quotes are mandatory.
474 <A REL="PARENT" HREF="..." > previous </A>
475 <A REL="PARENT PREVIOUS" HREF="..." > previous </A>
476 <A REL="SIBLING NEXT" HREF="..." > next </A>
477
478 4a. Legacy
479 The following are REL values which were known to be used as
480 values of the REL and REV attributes on the World Wide Web in
481 December 1995.
482
483 MADE
484 The REV=MADE relationship has been used to identify the author
485 or "maker" of an HTML document. Typical HREF values include a
486 Murray & Quin [Page 8]
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488 INTERNET DRAFT Hypertext Links in HTML December 1995
489 `mailto:' URI or the URL of the author's home page. Example:
490 <A REV=MADE HREF="mailto:murray@sq.com">Author</A>
491
492 NEXT/PREVIOUS/TOC/INDEX/NAVIGATOR
493 These values are described below, are used by SCO in its online
494 documentation and context- sensitive help system.
495
496 4b. Browser-defined Links
497
498 Some keywords are reserved and should not be used as REL/REV
499 values.
500
501 HTML user agents typically provide a mechanism for navigating
502 through the recent history of a user's access to documents;
503 traditionally these operations are referred to as "back" and
504 "forward". These mechanisms allow a user to step back through the
505 documents which led to the current location and then forward
506 again to retrace the path. Additionally, most user agents provide
507 a mechanism to immediately return to a user-defined location,
508 traditionally referred to as the home page, or "home". Since
509 these browser actions are internally implemented by the browser,
510 REL/REV keywords associated with these relationships are
511 disallowed.
512
513 HOME
514 RESERVED. Defined by the user (for example, using an
515 environment variable or preference, e.g. WWW_HOME).
516 This relationship may not be overridden; HTML user agents
517 should ignore any author-supplied REL=HOME setting.
518
519 BACK
520 RESERVED. Defined by the browser. This relationship may not
521 be overridden; HTML user agents should ignore any
522 author-supplied REL=BACK setting.
523
524 FORWARD
525 RESERVED. Defined by the browser. This relationship may not
526 be overridden; HTML user agents should ignore any
527 author-supplied REL=FORWARD setting.
528
529 4c. Navigational Node Links
530 Navigational nodes are commonly used document objects which are
531 designed by authors to assist the user in navigating through a
532 closed or extended document set. The most familiar and common
533 form of navigational node is a table of contents, which is a well
534 known publishing device used for enumerating and ordering the
535 contents of a closed document set.
536
537 CONTENTS or TOC
538 The TOC relationship identifies a Table of Contents.
539
540 When REL=TOC, the target document is the Table of Contents for
541 the current document, or for the collection of documents of
542 which the current document is a member.
543
544 When REV=TOC, the current document is a Table of Contents and
545 the target document is a related document.
546
547 Murray & Quin [Page 9]
548
549 INTERNET DRAFT Hypertext Links in HTML December 1995
550 When REL=TOC and REV=TOC it indicates that the current
551 document is a Table of Contents and the target document is
552 also a Table of Contents. Additional REL/REV values may be
553 used to specify the relationship between the two, such as
554 PARENT/CHILD.
555
556 If the hypertext link is specified with REL in a LINK element,
557 an HTML user agent may present an icon in a tool bar. Or, if
558 capable, an HTML user agent may present the Table of Contents
559 in a concurrent window or pane, highlighting the current
560 document.
561
562 INDEX
563 The INDEX relationship identifies an index.
564
565 When REL=INDEX, the target document is an index for the
566 current document, or for the collection of documents of which
567 the current document is a member.
568
569 When REV=INDEX, the current document is an index. Additional
570 REL/REV values may be used to further specify the relationship
571 between the two ends of the link.
572
573 If the hypertext link is specified with REL in a LINK element,
574 an HTML user agent may present an icon in a tool bar. An index
575 may be presented as an HTML document which is organized and
576 presented in a style reminiscent of a paper-based index. An
577 index may also be presented as a form-based query into a full-
578 text search database.
579
580 NAVIGATOR
581 The NAVIGATOR relationship identifies a navigational aid.
582
583 When REL=NAVIGATOR, the target document is a navigational aid.
584 A navigational aid may consist of a whole or partial Table of
585 Contents, a list of related documents, an indication of the
586 current document's location within a document hierarchy, or
587 any other information which may be useful to the user.
588
589 When REV=NAVIGATOR, the current document is a navigational aid.
590
591 If the hypertext link is specified with REL in a LINK element,
592 an HTML user agent may present an icon in a tool bar.
593
594 4d. Hierarchy Links
595 It is quite common for documents to be developed or defined
596 using a hierarchical model, or tree-like structure. The keywords
597 listed below may be used within HTML documents to identify the
598 hierarchical relationship of closely related nodes, such as the
599 immediate parent, siblings and children. In addition, the TOP
600 keyword may be used to identify the logical top (or root,
601 depending on your perspective) of a hierarchical or tree-like
602 structure.
603
604 The entire set of relationships may be used by a user agent to
605 build a map of the hierarchical structure(s) of which the
606 current document is a node. Hypertext links to documents
607 identified with PARENT and TOP values are more likely to be
608 Murray & Quin [Page 10]
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610 INTERNET DRAFT Hypertext Links in HTML December 1995
611 accessible through an icon or other mechanism than documents
612 identified with CHILD or SIBLING.
613
614 CHILD
615 The CHILD relationship identifies a subordinate or
616 subdocument. Any document may have multiple CHILD documents
617 within the same hierarchy.
618
619 When REL=CHILD, the target document is a hierarchical child,
620 or subdocument, of the current document.
621
622 When REV=CHILD, the current document is the hierarchical
623 child, or subdocument, of the target.
624
625 PARENT
626 The PARENT relationship identifies the superior or container
627 node.
628
629 When REL=PARENT, the target document is the hierarchical
630 parent, or container, of the current document.
631
632 When REV=PARENT, the current document is the hierarchical
633 parent, or container, of the target.
634
635 If the hypertext link is specified with REL in a LINK element,
636 an HTML user agent may present an icon in a tool bar.
637
638 SIBLING
639 The SIBLING relationship identifies a sibling in the current
640 hierarchy. Any document may have multiple SIBLING documents
641 within the same hierarchy.
642
643 When REL=SIBLING, the target document is a child of a common
644 parent, or a hierarchical peer of the current document. REL
645 and REV have equivalent meanings for the SIBLING
646 relationship.
647
648 TOP or ORIGIN
649 The TOP relationship identifies the logical top of a
650 hierarchical tree of which the current document is a branch.
651 BEGIN is a functional equivalent to TOP, if only one of these
652 values is specified.
653
654 When REL=TOP, the target document is the logical top node of
655 the tree. When REV=TOP, the current document is the logical
656 top of the tree.
657
658 If the hypertext link is specified with REL in a LINK element,
659 an HTML user agent may present an icon in a tool bar.
660
661 NOTE: ORIGIN has been suggested as an alternative to TOP to
662 provide metaphorical consistency with PARENT/CHILD/SIBLING.
663 Comments are encouraged.
664
665 4e. Sequence Links
666 Given a set of documents, it is possible and often desirable to
667 specify linear sequences to navigate through the set. A book, for
668 example, is often organized as a linear sequence. With sequence
669 Murray & Quin [Page 11]
670
671 INTERNET DRAFT Hypertext Links in HTML December 1995
672 links in each document, a user agent can step through or gather
673 an entire book programmatically.
674
675 BEGIN or FIRST
676 The BEGIN relationship identifies the author- defined start of
677 a sequence of documents of which the current document is a
678 node. TOP is a functional equivalent to BEGIN when only one of
679 these values is specified.
680
681 When REL=BEGIN, the target document is the beginning of the
682 sequence. When REV=BEGIN, the current document is the
683 beginning of the sequence.
684
685 If the hypertext link is specified with REL in a LINK element,
686 an HTML user agent may present an icon in a tool bar.
687 END or LAST
688 The END relationship identifies the author defined end of a
689 sequence of documents of which the current document is a node.
690 TOP is a functional equivalent to END when only one is
691 specified.
692
693 When REL=END, the target document is the end of the sequence.
694 When REV=END, the current document is the end of the sequence.
695
696 If the hypertext link is specified with REL in a LINK element,
697 an HTML user agent may present an icon in a tool bar.
698
699 NEXT
700 The NEXT relationship identifies the next document in an
701 author-defined sequence of documents, such as a linear book.
702
703 When REL=NEXT, the target document is next after the current
704 document. When REV=NEXT, the current document is next after
705 the target.
706
707 If the hypertext link is specified with REL in a LINK element,
708 an HTML user agent may present an icon in a tool bar.
709
710 PREVIOUS or PREV
711 The PREVIOUS relationship identifies the previous document in
712 an author-defined sequence of documents, such as a linear
713 book.
714
715 When REL=PREVIOUS, the target document is previous to the
716 current document.
717
718 When REV=PREVIOUS, the current document is previous to the
719 target.
720
721 If the hypertext link is specified with REL in a LINK element,
722 an HTML user agent may present an icon in a tool bar.
723
724 4f. Related Documents
725 BIBLIOENTRY
726 The BIBLIOENTRY relationship identifies a bibliographic entry.
727
728 BIBLIOENTRY would most typically be specified on an A element,
729 as it would specify a hypertext link between a citation and a
730 Murray & Quin [Page 12]
731
732 INTERNET DRAFT Hypertext Links in HTML December 1995
733 bibliographic entry describing the citation. Example:
734 <A REL=BIBLIOENTRY HREF="biblio.html#V.Bush"><CITE>As We
735 May Think</CITE></A>
736
737 The resource identified by this link may take any form desired
738 by the author/publisher. A bibliographic entry may be presented
739 in the style of a paper-based bibliographic entry, or it may be
740 presented as the result of a database query.
741
742 BIBLIOGRAPHY
743 The BIBLIOGRAPHY relationship identifies a bibliography.
744
745 The resource identified by this link may take any form desired
746 by the author/publisher. A bibliography may be presented as an
747 HTML document which is organized and presented in a style
748 reminiscent of a paper-based bibliography. A bibliography may
749 also be presented as a form-based query into a bibliographic
750 database.
751
752 If the hypertext link is specified with REL in a LINK element,
753 an HTML user agent may present a labeled icon in a tool bar.
754
755 CITATION
756 The CITATION relationship identifies a bibliographic citation.
757
758 When REL=CITATION, the target is a bibliographic citation. The
759 anchor, in this case, may be a bibliographic entry. The anchor
760 may also be a reference, thus allowing the reader a way to
761 locate the citation:
762 ... as described by Tim Berners-Lee
763 <A REL=CITATION HREF=#TBL>[1]</A>
764 ...
765
766 When REV=CITATION, the anchor is a citation. Typically, the
767 anchor would also be enclosed within a CITE element as shown in
768 the example below. The example shown here also corresponds to
769 the previous example, serving as its target by use of the NAME
770 attribute.
771 ... is described in Tim Berners-Lee's
772 <CITE><A NAME=TBL REV=CITATION HREF=./biblio/TBL > The
773 HyperText Markup Language </A> </CITE>
774 ...
775
776 NOTE: an alternative (and preferred) approach would be to add a
777 URI-valued attribute (HREF?) to the HTML CITE element.
778
779 DEFINITION
780 The DEFINITION relationship identifies a definition of a term.
781
782 Definitions may be, but are not necessarily, contained within a
783 glossary. DEFINITION would most typically be specified on an A
784 element, as it would specify a hypertext link from a term to
785 its definition.
786 <A REL=DEFINITION HREF="glossary.html#HTTP">HTTP</A>
787
788 FOOTNOTE
789 The FOOTNOTE relationship identifies a footnote.
790
791 Murray & Quin [Page 13]
792
793 INTERNET DRAFT Hypertext Links in HTML December 1995
794 When REL=FOOTNOTE is specified on an A element, the anchor is a
795 footnote marker and the target is a footnote. This can be used
796 to link from the footnote marker (or a highlighted word,
797 phrase, etc.) to an HTML document which contains the footnote
798 text, or to a portion of the same document (see REV=FOOTNOTE).
799
800 When REL=FOOTNOTE is specified on a LINK element, it can
801 specify a hypertext link to a set of footnotes which are
802 related to the current document, or to a set of end-notes.
803
804 When REV=FOOTNOTE is specified on an A element, the anchor is a
805 footnote; that is, the actual content of the footnote, as
806 opposed to a footnote marker. In this case, the target
807 specified by the HREF value, if any, is the footnote marker.
808
809 It has been suggested that the combination of REV=FOOTNOTE and
810 NAME=... on an A element may be used to imply that the
811 enclosed content not be rendered until a link to it is
812 explicitly traversed, at which time it can be presented in a
813 popup window. This would allow for the inclusion of footnote
814 text within a document that would not be visible until the
815 reader wanted it to be presented. Developers of user agents are
816 free to experiment with this proposed feature, but there is no
817 requirement that it be implemented.
818
819 GLOSSARY
820 The GLOSSARY relationship identifies a glossary.
821
822 When REL=GLOSSARY, the target document is a glossary. When
823 REV=GLOSSARY, the current document is a glossary.
824
825 If the hypertext link is specified with REL in a LINK element,
826 an HTML user agent may present an icon in a tool bar.
827
828 A glossary may be directly presented as an HTML document which
829 is organized and presented in a style reminiscent of a
830 paper-based glossary.
831
832 A glossary may also be accessed through an intermediary query
833 mechanism. For example, the user highlights a word or phrase
834 and presses the glossary button, thereby accessing the linked
835 object and passing the highlighted text as an argument. The
836 server returns the glossary entry relevant to the highlighted
837 word.
838
839 4g. Meta Documents
840 There are classes of information which are not intrinsic to a
841 document, but for which a clear and unambiguous association is
842 often useful or even necessary. This section defines a small set
843 of keywords which are related to ownership and legal notices.
844
845 Any attempt to rigorously define a closed set of meta- data
846 classes, types, and formats is doomed to failure, partly due to
847 the need for ongoing experimentation. Hence, the META keyword
848 may be used to identify meta documents which do not necesarily
849 have a clear or unambiguous definition. The content of the target
850 node may be as specific format as a MARC record or an FGDC
851 record, or it may be an author-defined format.
852 Murray & Quin [Page 14]
853
854 INTERNET DRAFT Hypertext Links in HTML December 1995
855
856 For each of the relationship keywords listed in this section, if
857 the relationship is specified with REL in a LINK element, an HTML
858 user agent may present a labeled icon in a tool bar.
859
860 AUTHOR
861 The AUTHOR relationship identifies a hypertext link to
862 an author.
863
864 The hypertext link may be to the author's home page, a
865 biography, an audio or video clip, or an agent which sends mail
866 to the author (e.g., using the `mailto:' scheme).
867
868 COPYRIGHT
869 The COPYRIGHT relationship identifies a hypertext link to a
870 copyright notice.
871
872 While it is arguable whether a copyright notice is required in
873 every HTML file to assert copyright protection on it, there is
874 clearly a desire to express copyright notice among a sufficient
875 portion of the user community to justify support.
876
877 A basic copyright notice for this document may simply state:
878 "Copyright 1995 by Murray C. Maloney". It may be desirable,
879 in place of or in addition to such a notice, to have a
880 hypertext link between each HTML document in a set and a single
881 copyright notice, as in the following examples:
882 <LINK REL=COPYRIGHT HREF="copyright.html">
883 <A REL=COPYRIGHT HREF="copyright.html">
884 Copyright 1995 by Murray C. Maloney</A>
885
886 DISCLAIMER
887 The DISCLAIMER relationship identifies a hypertext link to a
888 legal disclaimer. Usage is expected to be similar to that of
889 the COPYRIGHT hypertext link. As with the copyright notice,
890 there is no intention or expectation that such a link would be
891 the only way to express a disclaimer.
892
893 EDITOR
894 The EDITOR relationship identifies a hypertext link to an
895 editor. Usage is expected to be similar to that of the AUTHOR
896 hypertext link.
897
898 META
899 The META relationship identifies a hypertext link to a node
900 which contains meta-information related to the current
901 document. This is intended to be a generalized meta-data
902 relationship descriptor.
903
904 PUBLISHER
905 The PUBLISHER relationship identifies a hypertext link to a
906 publisher. Usage is expected to be similar to that of the
907 AUTHOR hypertext link.
908
909 TRADEMARK
910 The TRADEMARK relationship identifies a hypertext link to a
911 trademark notice. Usage is expected to be similar to that of
912 the COPYRIGHT hypertext link.
913 Murray & Quin [Page 15]
914
915 INTERNET DRAFT Hypertext Links in HTML December 1995
916
917 4f. Other REL and REV Values Under Discussion
918 The POINTER keyword is an invention of the author.
919
920 The BANNER, BOOKMARK, HOTLIST and STYLESHEET keywords are
921 described in Dave Raggett's Internet Draft on HTML 3.0. Recent
922 discussions tend to indicate that these keywords may not be
923 appropriate for use as REL/REV values. Dave Raggett's further
924 explanation and justification is needed before any further
925 discussion or decision can be made as to the future status of
926 these keywords.
927
928 The LANG attribute is described in Dave Raggett's Internet Draft
929 on HTML 3.0. It has been applied to various HTML elements, not
930 including the LINK and A elements. The author suggests that LANG
931 is a useful attribute to apply to the LINK and A elements. See
932 also the discussion of REL=TRANSLATION.
933
934 BANNER
935 The BANNER relationship identifies a document banner.
936
937 When REL=BANNER, the target document is to be included within
938 the current document as a banner. A banner is typically used
939 for corporate logos, custom toolbars, and other information
940 which would not typically be scrolled with the body of a
941 document.
942
943 When REV=BANNER, the current document is a banner. This may be
944 used, in future, to provide error-checking or to prevent the
945 use of a document as a banner unless it has been explicitly
946 identified as a valid source. (Or not! Sorry, I was reaching
947 for a useful meaning.)
948
949 Compelling arguments have been made against the need for a
950 REL=BANNER value, which is simply a special case of the INCLUDE
951 mechanism.
952 BOOKMARK
953 The BOOKMARK relationship identifies a bookmark.
954
955 Bookmarks are used to provide direct links to key entry points
956 into an extended document. The TITLE attribute may be used to
957 label the bookmark. Several bookmarks may be defined in each
958 document, and provide a means for orienting users in extended
959 documents.
960
961 HOTLIST
962 RESERVED: This keyword has been proposed by Dave Raggett. Its
963 meaning and purpose require further explanation. A placeholder
964 is being maintained until such time as Dave has had an
965 opportunity to provide further explanation, examples,
966 discussion and justification.
967
968 If the hypertext link is specified with REL in a LINK element,
969 an HTML user agent may present an icon in a tool bar.
970
971 LANG
972 The LANG attribute indicates the language of the target
973 document.
974 Murray & Quin [Page 16]
975
976 INTERNET DRAFT Hypertext Links in HTML December 1995
977
978 The LANG attribute is optional and has no default value. It may
979 be used for purely informational purposes by an HTML user
980 agent, or by a robot for language classification.
981
982 Used in combinatiuon with a proposed REL=TRANSLATION and a
983 user's language preference setting, an HTML user agent may
984 intelligently select from a collection of otherwise equivalent
985 hypertext links expressed with the LINK element. If the user's
986 language preference is not available, the user agent may
987 present a virtual menu of language options.
988
989 See the Internet Draft on the Internatiolisation of HTML for
990 a definition of the values of this attribute.
991
992 POINTER
993 The pointer relationship identifies a hypertext pointer. That
994 is, this is a way to do indirection in HTML.
995
996 When REV=POINTER, the anchor is a pointer to the target
997 document. When a hypertext link is traversed to a LINK or A
998 element with REV=POINTER, the target specified by the HREF
999 value should be traversed, and so on, until a target without
1000 REV=POINTER is retrieved.
1001 <LINK NAME=PSEUDO REV=POINTER HREF="real.html">
1002
1003 When REL=POINTER, the target is a pointer to the real target.
1004 This value can be used by a user agent to perform a pre-fetch
1005 of the specified target for evaluation until the real target is
1006 reached.
1007
1008 NOTE: The authors propose that the NAME attribute be removed
1009 from the LINK element, or that a practical use for it should be
1010 defined. For example, hypertext indirection can be specified by
1011 providing both a NAME and an HREF value on the LINK element, in
1012 combination with a specific REL or REV value, such as POINTER.
1013 Some support exists among members of the HTML Working Group to
1014 provide for hypertext indirection with the LINK element. There
1015 is no other reason for an author to define a target by using
1016 the NAME attribute on a LINK element, since the resulting
1017 target address is functionally equivalent to the address of the
1018 document in which such a target is defined.
1019
1020 STYLESHEET
1021 The STYLESHEET relationship identifies a stylesheet.
1022
1023 When REL=STYLESHEET, the target document is a stylesheet. When
1024 associated with a LINK element, the author/publisher is
1025 expressing an expectation that the target stylesheet will be
1026 applied by the HTML user agent. When associated with an A
1027 element, an HTML user agent may simply retrieve the target
1028 stylesheet for display, or it may launch a stylesheet editor
1029 with the target stylesheet.
1030
1031 When REV=STYLESHEET, the current document is a stylesheet and
1032 the target document may be a demonstration of its use. In
1033 general, it is not anticipated that stylesheets will contain
1034 LINK or A elements, as they are not projected to be HTML
1035 Murray & Quin [Page 17]
1036
1037 INTERNET DRAFT Hypertext Links in HTML December 1995
1038 documents.
1039
1040 TRANSLATION
1041 The TRANSLATION relationship specifies a translation to
1042 another language.
1043
1044 When REL=TRANSLATION, the target is a translation to another
1045 language. This value will most typically be used with the LINK
1046 element, in combination with specification of the target
1047 document's language as a LANG attribute value. Presumably,
1048 REL=TRANSLATION can be used with the A element to specify a
1049 translation of a document fragment, such as a phrase in a
1050 foreign language.
1051
1052 When REV=TRANSLATION, the current document, or document
1053 fragment, is a translation of the target.
1054
1055 URC
1056 The URC relationship identifies a Uniform Resource Catalogue
1057 for the current document.
1058
1059 This keyword has been proposed by Dave Raggett. Its meaning
1060 and purpose have not been explained to the author, but a
1061 placeholder is being maintained until such time as Dave has had
1062 an opportunity provide explanation, examples,
1063 discussion and justification.
1064
1065 5. Hypertext Includes
1066 There have been many discussions in various forums which clearly
1067 indicate that hypertext includes are a desired feature of the HTML
1068 language, and for which widespread user agent support is needed.
1069
1070 There are, apparently, three popular syntactic approaches to
1071 inclusion: specifying INCLUDE as REL value on the A and LINK
1072 elements, specifying a newly-defined and specially- purposed INCLUDE
1073 element (which would presumably also have REL and REV attributes),
1074 and using SGML entities. Each is described and discussed below, but
1075 no arguments are presented.
1076
1077 In either case, there is an expectation that processing of an
1078 INCLUDE link would result in the INCLUDE value being deleted from the
1079 REL list and inserted into the REV list. In other words, a
1080 REL=INCLUDE indicates that the inclusion has yet to happen, while a
1081 REV=INCLUDE indicates that the inclusion has already happened. It is
1082 helpful, for legal and copyright purposes, that included material be
1083 identifiable at all times.
1084
1085 Note that the form of inclusion referred to here is also known as
1086 Transclusion, or as client side inclusion. It may happen either
1087 automatically, when a document is loaded into an HTML client,
1088 or explicitly: for example when the user selects an icon, included
1089 text may appear at that point in the current document.
1090
1091 5a. INCLUDE as a REL or REV Value
1092 INCLUDE relationship identifies a document for inclusion.
1093
1094 When REL=INCLUDE, the target document should be included at the
1095 anchor location. This value is typically, though not always, used
1096 Murray & Quin [Page 18]
1097
1098 INTERNET DRAFT Hypertext Links in HTML December 1995
1099 with the A element. Using this value on a LINK element implies
1100 that the included document only contains information which is
1101 valid within the HEAD of an HTML document.
1102
1103 When REV=INCLUDE, the current document is identifying itself as an
1104 included document in the target document.
1105
1106 5b. INCLUDE as an Element
1107 An anchor may also be specified using a newly-defined INCLUDE
1108 element:
1109 <INCLUDE REL=INCLUDE HREF="boilerplate.html"></INCLUDE>
1110
1111 In this scheme, when the hypertext link is traversed, and the
1112 content of the target document is included, the INCLUDE element
1113 would surround the included text. As a function of traversing the
1114 link, the REL attribute value would be transformed to a REV value,
1115 thus maintaining information about the link.
1116 <INCLUDE REV=INCLUDE HREF="boilerplate.html">
1117 This is the boilerplate text
1118 </INCLUDE>
1119
1120 5c. SGML external entitities
1121 SGML provides a mechanism for specifying external entities and
1122 including them, by reference, in an SGML document.
1123
1124 Unfortunately, the current HTML browser technology cannot easily
1125 support the use of SGML entities, and they cannot be used in
1126 a way that is completely backwards-compatible with existing
1127 software.
1128
1129 6. Hypertext Paths
1130 NOTE: Recent discussions tend to indicate that the mechanisms and
1131 language uses needed to support paths have not been adequately
1132 articulated or specified. This section appears here for historical
1133 completeness. Dave Raggett's further explanation and justification is
1134 needed before any further discussion or decision can be made as to
1135 the future status of these keywords.
1136
1137 Paths are described briefly in Dave Raggett's Internet Draft on HTML
1138 3.0, and reproduced below without further explanation. Further
1139 discussion, explanation and justification from Dave are clearly
1140 required before any further public discussion or decision can be
1141 made as to the future status of these keywords. The material below
1142 is reproduced for historic purposes and may be subject to future
1143 revision.
1144
1145 Values for use in defining Guided Tours with <A> element. These
1146 allow Guided Tours to be defined using HTML, for instance as part of
1147 tables of contents, for example:
1148 <A REL=NODE REV=TOC HREF="Chap1.html">
1149
1150 NODE
1151 The NODE relationship implies PREVIOUS/NEXT LINKs for given URI.
1152
1153 PATH
1154 The PATH relationship specifies that the given URI contains <A
1155 REL=NODE> links that should be inserted into the guided tour.
1156
1157 Murray & Quin [Page 19]
1158
1159 INTERNET DRAFT Hypertext Links in HTML December 1995
1160 The browser treats the REL=NODE URIs as forming a sequence of
1161 nodes to follow and sets the <LINK REL=PREVIOUS>, NEXT as
1162 appropriate for each node as it is visited.
1163
1164 7. Proposed New Attributes for A and LINK Elements
1165
1166 Through the course of discussions, suggestions have been made to
1167 create new attributes for the LINK and/or A elements. These are
1168 preliminary discussions, with no sample implementations to
1169 demonstrate support.
1170
1171 7a. ACTION or STYLE or PROCESS or PRESENT
1172 Activating a link in the HTML user agents of mid-1995 typically
1173 results in the linked object replacing the current object in the
1174 presentation window of the user agent. By convention, HTML user
1175 agents typically provide an alternate method which spawns another
1176 window and presents the linked object in it.
1177
1178 It has been suggested by Ian Graham and Roy Fielding, and agreed
1179 upon by many others, that the author should have some means to
1180 indicate a preference for the manner in which the user agent
1181 should present the linked object to the user. As you can see, the
1182 name of the attribute still needs to be settled.
1183
1184 From Ian Graham: It seems reasonable to allow the
1185 author to suggest browser behavior when links are activated.
1186 For example, when I click on a LINK button, should I clone a
1187 window for the link, or pop up a subwindow for a glossary
1188 entry? Perhaps this should be part of a CLASS attribute, but
1189 to my mind CLASS should be used to define the
1190 presentation/meaning of a document element in the document BODY
1191 as opposed to browser behavior.
1192
1193 And from Roy Fielding: Presentation semantics -- where should
1194 the results be "placed". A `STYLE=""' attribute (defined as
1195 SGML NAMES) would do nicely here.
1196
1197 Possible values and their meanings are:
1198 CLONE
1199 Present the linked object in a presentation window which is a
1200 clone of the current presentation window. That is popup another
1201 persistent window.
1202
1203 See the Netscape Frames proposal for one way to do this, using
1204 named windows and the TARGET attribute described below.
1205
1206 EMBED
1207 Present the linked object at the current location. This
1208 provides a syntax for expressing "stretch text", but it also
1209 presents numerous problems. This will be subject to much
1210 debate. See the section on Include, above.
1211
1212 REPLACE
1213 The default behavior. Present the linked object in the current
1214 presentation window, replacing the current object completely.
1215
1216 POPUP
1217 Present the linked object in a non-persistent presentation
1218 Murray & Quin [Page 20]
1219
1220 INTERNET DRAFT Hypertext Links in HTML December 1995
1221 window. That is, show the linked object while the user is
1222 activating the link, and make it disappear when the user
1223 releases activation. In the case that the popup is entered
1224 without user activation, the user agent may provide a "Cancel"
1225 button or another mechanism to make the popup window
1226 disappear.
1227
1228 SPLITSCREEN or HORSPLIT
1229 Present the linked object in one pane of a horizontally split
1230 window.
1231
1232 ALONGSIDE or VERSPLIT
1233 Present the linked object in one pane of a vertically split
1234 window.
1235
1236 7b. TARGET
1237 Netscape Corporation have proposed to add a TARGET attribute to
1238 the A element; its value is the name of the window in which to
1239 display the result of following the link.
1240
1241 This is most useful in conjunction with a mechanism (such as
1242 FRAMES, not discussed in this document) to give names to windows.
1243 However, if no window exists with the given name, a reasonable
1244 action is to create such a window.
1245
1246 An HTML client in a non-windowing environment would have to find
1247 some way to indicate the presence of multuple active document areas,
1248 and to allow navigation amongst them.
1249
1250 7c. DINGBAT
1251 The DINGBAT attribute, applied to the LINK element and the A
1252 element, would be used to specify the entity name of a graphic
1253 image (an icon) to associate with a hypertext link. The DINGBAT
1254 attribute values must be specified by the HTML DTD as an SGML name
1255 token group.
1256
1257 When used with LINK, the icon may be used on an HTML user agent
1258 toolbar. When used with A, the icon may be placed in close
1259 proximity to the anchor's highlighted text, as a footnote marker
1260 for example.
1261
1262 There are advantages to using an entity rather than an external
1263 graphic. Presumably, a user agent would pre-load the standard set
1264 of entities, thereby eliminating the need to fetch a graphic
1265 across the network. It is hoped that user agents will provide
1266 users with a means to specify the system location of personalized
1267 or customized versions of standard icons, thereby offering the
1268 user the opportunity to exercise greater control over the user
1269 interface and the graphical presentation.
1270
1271 The DINGBAT attribute has already been proposed for lists and list
1272 items in Dave Raggett's Internet Draft on HTML 3.0. User agent
1273 behavior, in the face of contention between DINGBAT and SRC, must
1274 be specified.
1275
1276 7d. HILITE or HIGHLIGHT
1277 Roy Fielding has pointed out that the author can
1278 indicate a preference for the style of anchor
1279 Murray & Quin [Page 21]
1280
1281 INTERNET DRAFT Hypertext Links in HTML December 1995
1282 highlighting. So far, the list of candidate
1283 keywords are:
1284 * None
1285 * Button
1286 * IconOnly
1287 * Underline
1288 * Outline
1289 * Reverse
1290
1291 7e. METHOD
1292 From Ian Graham: It would often be convenient to
1293 access a link using a defined HTTP method other than GET. For
1294 example, suppose I have a LINK attribute defining a related,
1295 searchable glossary. One desirable behavior is as follows: the
1296 user highlights a word and clicks a mouse button (or presses a
1297 glossary button). The browser accesses the linked object, passing
1298 to it the highlighted text. The server then returns the glossary
1299 entry relevant to the highlighted word. This requires
1300 standardised methods and data encoding schemes. There is only one,
1301 namely the HTTP TEXTSEARCH method, which is how ISINDEX search
1302 queries are sent to a server. I therefore propose that the METHOD
1303 attribute have two possible values, namely GET|TEXTSEARCH, to
1304 indicate how the client should access the linked resource.
1305
1306 7f. SRC
1307 The SRC attribute, applied to the LINK element and the A element,
1308 would be used to specify the location of a file containing a
1309 graphic image (an icon) to associate with a hypertext link. When
1310 used with LINK, the icon may be used on an HTML user agent
1311 toolbar. When used with A, the icon may be placed in close
1312 proximity to the anchor's highlighted text, as in the case of a
1313 footnote marker for example.
1314
1315 This extension of the applicability of the SRC attribute has
1316 already been proposed for lists, list items, and admonishments in
1317 Dave Raggett's Internet Draft on HTML 3.0. User agent behavior
1318 remains to be specified in the face of contention between DINGBAT
1319 and SRC attributes.
1320
1321 7g. WHEN
1322 Roy Fielding and Ian Graham have pointed out that user agents
1323 currently exhibit different behavior between their processing of
1324 hypertext links specified with the SRC attribute and those
1325 specifiewd with HREF. Typically, user agents await user activation
1326 before traversing a hypertext link specified with an HREF
1327 attribute, while those specified with SRC are more often fetched
1328 immediately. This distinction is a natural consequence of a
1329 design which uses the SRC attribute to specify a hypertext link to
1330 an embedded graphical image.
1331
1332 The author can take advantage of an ability to specify when, or
1333 the type of event, which should initiate the hypertext link.
1334
1335 Roy Fielding suggested the following possible attribute values:
1336 UserSelect as is the case for anchors and FORMS
1337 AutoEntry as is the case for EMBED or IMG
1338 AutoExit an interesting derivative
1339 Export only used external to the user process
1340 Murray & Quin [Page 22]
1341
1342 INTERNET DRAFT Hypertext Links in HTML December 1995
1343
1344 In response, Murray Maloney asked: Would the AutoExit derivative
1345 provide a means for me to do indirection? For example, in
1346 document A I have <A HREF=B#foo>, and in B I have <LINK NAME=foo
1347 STYLE=AutoExit HREF=C>. Would asserting the anchor in A lead me
1348 to C? If so, wonderful. If not, then why not and what then?
1349
1350 Please explain the meaning of "Export"? That is, if I use it what
1351 does it imply about "when should the action take place"?
1352
1353 (Liam Quin things Export doesn't imply any action at all, but
1354 doesn't yet understand why it might be useful)
1355
1356 Consider these examples:
1357 <LINK ACTION=POPUP WHEN=AutoEntry
1358 REL=COPYRIGHT HREF="copyright.html">
1359 <A ACTION=POPUP WHEN=AutoEntry
1360 REL=COPYRIGHT HREF="copyright.html">
1361 Copyright 1995 by Murray C. Maloney</A>
1362 In either case, the user agent is expected to display the target
1363 document in a popup as soon as the current document is retrieved.
1364
1365 7h. OBSOLETES, UPDATES and DERIVED-FROM:
1366 Roy Fielding also suggested the following relations:
1367 OBSOLETES
1368 when REL=OBSOLETES, the target document is a later version of
1369 the current document; when REV=OBSOLETES, the target document
1370 is obsoleted by the current document.
1371
1372 UPDATES
1373 When REL=UPDATES, the target document contains revisions to the
1374 current document (would REVISES be clearer?).
1375
1376 DERIVED-FROM
1377 When REL=DERIVED-FROM, the target document was derived from the
1378 current document; when REV=DERIVED-FROM, the current document
1379 was derived from the target document, perhaps by automatic
1380 processing or by manual editing.
1381
1382 8. Acknowledgements
1383 This paper is the synthesis and codification of ideas from
1384 a variety of sources. It is only fitting that those who
1385 have contributed to the discussion in various forums should
1386 be acknowledged for their part in the recent attempt to
1387 move this work forward.
1388 Terry Allen, O'Reilly and Associates, terry@ora.com
1389 Murray M. Altheim, NTTC, murray.altheim@nttc.edu
1390 Brian Behlendorf, Indiana Univ., brian@organic.com
1391 Bert Bos, Rijksuniversiteit Groningen, bert@let.rug.nl
1392 Jon Bosak, Novell, Jon Bosak@novell.com
1393 Henry Budgett, SCO, henryb@sco.com
1394 Paul Burchard, burchard@geom.umn.edu
1395 Dan Connolly, MIT/W3C, connolly@w3.org
1396 Steve DeRose, Electronic Book Technologies, steve@ebt.com
1397 Joe English, joe@trystero.art.com
1398 Roy T. Fielding, Univ. of California (Irvine), fielding@ics.uci.edu
1399 Peter Flynn, pflynn@curia.ucc.ie
1400 Ian Graham, Univ. of Toronto, igraham@utirc.utoronto.ca
1401 Murray & Quin [Page 23]
1402
1403 INTERNET DRAFT Hypertext Links in HTML December 1995
1404 Dave Hollander, HP, dmh@hpsgml.fc.hp.com
1405 Alex Hopmann, ResNova Software, Inc., hopmann@holonet.net
1406 Craig Hubley, Craig Hubley & Associates, craig@passport.ca
1407 Albert Lunde, Albert-Lunde@nwu.edu
1408 Tom Magliery, NCSA, mag@ncsa.uiuc.edu
1409 Eve Maler, ArborText, eve@doctools.com
1410 Larry Masinter, Xerox, masinter@parc.xerox.com
1411 Eric Miller, OCLC, emiller@oclc.org
1412 Lou Montulli, Netscape Communications, montulli@netscape.com
1413 David Morris, dwm@shell.portal.com
1414 Dave Raggett, MIT/W3C, dsr@w3.org
1415 Bob Stayton, SCO, bobs@sco.com
1416 Stu Weibel, OCLC, weibel@oclc.org
1417 Faith Zack, SCO, faithz@sco.com
1418

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