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2 Network Working Group M. Nottingham
3 Internet-Draft February 25, 2009
4 Updates: 4287 (if approved)
5 Intended status: Standards Track
6 Expires: August 29, 2009
8 Link Relations and HTTP Header Linking
9 draft-nottingham-http-link-header-04
11 Status of this Memo
13 This Internet-Draft is submitted to IETF in full conformance with the
14 provisions of BCP 78 and BCP 79. This document may contain material
15 from IETF Documents or IETF Contributions published or made publicly
16 available before November 10, 2008. The person(s) controlling the
17 copyright in some of this material may not have granted the IETF
18 Trust the right to allow modifications of such material outside the
19 IETF Standards Process. Without obtaining an adequate license from
20 the person(s) controlling the copyright in such materials, this
21 document may not be modified outside the IETF Standards Process, and
22 derivative works of it may not be created outside the IETF Standards
23 Process, except to format it for publication as an RFC or to
24 translate it into languages other than English.
26 Internet-Drafts are working documents of the Internet Engineering
27 Task Force (IETF), its areas, and its working groups. Note that
28 other groups may also distribute working documents as Internet-
29 Drafts.
31 Internet-Drafts are draft documents valid for a maximum of six months
32 and may be updated, replaced, or obsoleted by other documents at any
33 time. It is inappropriate to use Internet-Drafts as reference
34 material or to cite them other than as "work in progress."
36 The list of current Internet-Drafts can be accessed at
37 http://www.ietf.org/ietf/1id-abstracts.txt.
39 The list of Internet-Draft Shadow Directories can be accessed at
40 http://www.ietf.org/shadow.html.
42 This Internet-Draft will expire on August 29, 2009.
44 Copyright Notice
46 Copyright (c) 2009 IETF Trust and the persons identified as the
47 document authors. All rights reserved.
49 This document is subject to BCP 78 and the IETF Trust's Legal
50 Provisions Relating to IETF Documents in effect on the date of
51 publication of this document (http://trustee.ietf.org/license-info).
52 Please review these documents carefully, as they describe your rights
53 and restrictions with respect to this document.
55 Abstract
57 This document specifies relation types for Web links, and defines a
58 registry for them. It also defines how to send such links in HTTP
59 headers with the Link header-field.
61 Table of Contents
63 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
64 2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 3
65 3. Links . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
66 4. Link Relation Types . . . . . . . . . . . . . . . . . . . . . 4
67 5. The Link Header Field . . . . . . . . . . . . . . . . . . . . 5
68 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
69 7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
70 8. Internationalisation Considerations . . . . . . . . . . . . . 11
71 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
72 9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
73 9.2. Informative References . . . . . . . . . . . . . . . . . . 12
74 Appendix A. Notes on Using the Link Header with HTML4 . . . . . . 13
75 Appendix B. Notes on Using the Link Header with Atom . . . . . . 14
76 Appendix C. Acknowledgements . . . . . . . . . . . . . . . . . . 15
77 Appendix D. Document history . . . . . . . . . . . . . . . . . . 15
78 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17
80 1. Introduction
82 A means of indicating the relationships between resources on the Web,
83 as well as indicating the type of those relationships, has been
84 available for some time in HTML [W3C.REC-html401-19991224], and more
85 recently in Atom [RFC4287]. These mechanisms, although conceptually
86 similar, are separately specified. However, links between resources
87 need not be format-specific; it can be useful to have typed links
88 that are independent of the format, especially when a resource has
89 representations in multiple formats.
91 To this end, this document defines a framework for typed links that
92 isn't specific to a particular serialisation or context of use. It
93 does so by re-defining the link relation registry established by Atom
94 to have a broader scope, and adding to it the relations that are
95 defined by HTML.
97 Furthermore, an HTTP header-field for conveying typed links was
98 defined in [RFC2068], but removed from [RFC2616], due to a lack of
99 implementation experience. Since then, it has been implemented in
100 some User-Agents (e.g., for stylesheets), and several additional use
101 cases have surfaced. Because it was removed, the status of the Link
102 header is unclear, leading some to consider minting new application-
103 specific HTTP headers instead of reusing it. This document addresses
104 this by re-specifying the Link header with updated but backwards-
105 compatible syntax.
107 [[ Feedback is welcome on the ietf-http-wg@w3.org mailing list,
108 although this is NOT a work item of the HTTPBIS WG. ]]
110 2. Notational Conventions
112 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
113 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
114 document are to be interpreted as described in BCP 14, [RFC2119], as
115 scoped to those conformance targets.
117 This document uses the Augmented Backus-Naur Form (ABNF) notation of
118 [RFC2616], and explicitly includes the following rules from it:
119 quoted-string, token, SP (space). Additionally, the following rules
120 are included from [RFC3986]: URI and URI-Reference, and from
121 [RFC4288]: type-name.
123 3. Links
125 In this specification, a link is a typed connection between two
126 resources that are identified by IRIs [RFC3987], and is comprised of:
127 o A context IRI, and
128 o A link relation type (Section 4), and
129 o A target IRI.
131 A link can be viewed as a statement of the form "(context IRI) has a
132 (relation type) resource at (target IRI)."
134 Note that in the common case, the context IRI will also be a URI
135 [RFC3986], because common protocols (such as HTTP) do not support
136 dereferencing IRIs. Likewise, the target IRI will be converted to a
137 URI in serialisations that do not support IRIs (e.g., the Link
138 header).
140 This specification does not place restrictions on the cardinality of
141 links; there can be multiple links from and to a particular IRI, and
142 multiple links of different types between two given IRIs.
144 Additionally, this specification does not define a general syntax for
145 expressing links, nor mandate a specific context for any given link;
146 it is expected that applications of links will specify both aspects.
147 One such application is communication of links through HTTP headers,
148 specified in Section 5.
150 Such applications may further constrain or extend links (e.g.,
151 associating a media type hint).
153 4. Link Relation Types
155 A link relation type identifies the semantics of a link. For
156 example, a link with the relation type "copyright" indicates that the
157 resource identified by the target IRI is a statement of the copyright
158 terms applying to the current context IRI.
160 Relation types are not to be confused with media types [RFC4288];
161 they do not identify the format of the representation that results
162 when the link is dereferenced. Rather, they only describe how the
163 current context is related to another resource.
165 As such, relation types are not format-specific, and MUST NOT specify
166 a particular format or media type that they are to be used with.
167 Likewise, the context IRI for a given link is usually determined by
168 the serialisation of the link (e.g., the Link header, a HTML
169 document, etc.); a relation type SHOULD NOT specify the context IRI.
171 Consuming implementations SHOULD ignore relation types that they do
172 not understand or have no need to process.
174 There are two kinds of relation types; registered and extension.
176 4.1. Registered Relation Types
178 Commonly-used relation types with a clear meaning that are shared
179 across applications can be registered as tokens for convenience and
180 to promote reuse. For example, "self" and "alternate" are registered
181 relation types, because they are broadly useful.
183 This draft establishes an IANA registry of such relation types; see
184 Section 6.2.
186 Registered relation types MUST conform to the token rule, and SHOULD
187 conform to the sgml-name rule for compatibility with deployed
188 implementations;
190 sgml-name = ALPHA *( ALPHA | DIGIT | "." | "-" )
192 Names that differ only in case from existing entries (e.g., "Foo" and
193 "foo") MUST NOT be registered.
195 Registered relation types MUST be compared in a case-insensitive
196 fashion.
198 Although they are specified as tokens, applications wishing to
199 internally refer to an extension relation type using a URI MAY do so
200 by considering it relative to the base URI
201 "http://www.iana.org/assignments/relation/". However, the URI form
202 of a registered relation type SHOULD NOT be serialised when an
203 application specifies the use of a relation type, because a consuming
204 implementation may not recognise it.
206 4.2. Extension Relation Types
208 Applications that don't merit a registered relation type may use an
209 extension relation type. An extension relation type is a URI
210 [RFC3986] that, when dereferenced, SHOULD yield a document describing
211 that relation type.
213 Extension relation types MUST be compared in a case-sensitive
214 fashion, character-by-character.
216 5. The Link Header Field
218 The Link entity-header field provides a means for conveying one or
219 more links in HTTP headers. It is semantically equivalent to the
220 element in HTML, as well as the atom:link feed-level element
221 in Atom [RFC4287].
223 Link = "Link" ":" #link-value
224 link-value = "<" URI-Reference ">" *( ";" link-param ) )
225 link-param = ( ( "rel" "=" relation-types )
226 | ( "rev" "=" relation-types )
227 | ( "type" "=" type-name )
228 | ( "title" "=" quoted-string )
229 | ( "title*" "=" enc2231-string )
230 | ( "anchor" "=" <"> URI-Reference <"> )
231 | ( link-extension ) )
232 link-extension = token [ "=" ( token | quoted-string ) ]
233 enc2231-string = ,
234 Section 7>
235 relation-types = relation-type |
236 <"> relation-type *( SP relation-type ) <">
237 relation-type = reg-relation-type | ext-relation-type
238 reg-relation-type = token
239 ext-relation-type = URI
241 For example:
243 Link: ; rel="previous";
244 title="previous chapter"
246 indicates that chapter2 is previous to this resource in a logical
247 navigation path.
249 Each link-value conveys one target IRI as a URI-Reference (after
250 conversion, if necessary) inside angle brackets ("<>"). If the URI-
251 Reference is relative, it MUST be resolved as per [RFC3986]. Note
252 that any base IRI from the body's content is not applied.
254 By default, the context of a link conveyed in the Link header field
255 is the IRI associated with the representation it occurs in. When
256 present, the anchor parameter overrides this with another URI, such
257 as a fragment of this resource, or a third resource (i.e., when the
258 anchor value is an absolute URI).
260 Normally, the relation type of a link is conveyed in the "rel"
261 parameter's value. The "rev" parameter has also been used for this
262 purpose historically by some formats, and is included here for
263 compatibility with those uses, but its use is not encouraged nor
264 defined by this specification.
266 Note that extension relation types are REQUIRED to be absolute URIs
267 in Link headers, and MUST be quoted if they contain a semicolon (";")
268 or comma (",").
270 The title parameter is used to label the destination of a link such
271 that it can be used as a human-readable identifier (e.g. a menu
272 entry). The title* parameter MAY be used to instead to encode this
273 label in an alternate character set, and/or contain language
274 information as per [RFC2231]. When using the enc2231-string syntax,
275 producers MUST NOT use a charset value other than 'ISO-8859-1' or
276 'UTF-8'.
278 Note that link-values may convey multiple links between the same
279 target and context IRIs; for example
281 Link: ; rel=index;
282 rel="start http://example.net/relation/other"
284 Here, the link to "http://example.org/" has the registered relation
285 types "index" and "start", and the extension relation type
286 "http://example.net/relation/other".
288 6. IANA Considerations
290 6.1. Link Header Registration
292 This specification updates the Message Header Registry entry for
293 "Link" in HTTP [RFC3864] to refer to this document.
295 Header field: Link
296 Applicable protocol: http
297 Status: standard
298 Author/change controller:
299 IETF (iesg@ietf.org)
300 Internet Engineering Task Force
301 Specification document(s):
302 [ this document ]
304 6.2. Link Relation Type Registry
306 This specification establishes the Link Relation Type Registry,
307 located at , and updates
308 Atom [RFC4287] to refer to it in place of the "Registry of Link
309 Relations".
311 The requirements for registered relation types are described in
312 Section 4.1.
314 Relation types may be registered on the advice of a Designated Expert
315 (appointed by the IESG or their delegate), with a Specification
316 Required (using terminology from [RFC5226]).
318 Registration requests consist of the completed registration template
319 below, typically published in an RFC or Open Standard (in the sense
320 described by [RFC2026], section 7). However, to allow for the
321 allocation of values prior to publication, the Designated Expert may
322 approve registration once they are satisfied that an RFC (or other
323 Open Standard) will be published.
325 The registration template is:
327 o Relation Name:
328 o Description:
329 o Reference:
331 Upon receiving a registration request (usually via IANA), the
332 Designated Expert should request review and comment from the
333 apps-discuss@ietf.org mailing list (or a successor designated by the
334 APPS Area Directors). Before a period of 30 days has passed, the
335 Designated Expert will either approve or deny the registration
336 request, communicating this decision both to the review list and to
337 IANA. Denials should include an explanation and, if applicable,
338 suggestions as to how to make the request successful.
340 The Link Relation Type registry's initial contents are:
342 o Relation Name: alternate
343 o Description: Designates a substitute for the link's context.
344 o Reference: [W3C.REC-html401-19991224]
346 o Relation Name: appendix
347 o Description: Refers to an appendix.
348 o Reference: [W3C.REC-html401-19991224]
350 o Relation Name: bookmark
351 o Description: Refers to a bookmark or entry point.
352 o Reference: [W3C.REC-html401-19991224]
354 o Relation Name: chapter
355 o Description: Refers to a chapter in a collection of resources.
356 o Reference: [W3C.REC-html401-19991224]
358 o Relation Name: contents
359 o Description: Refers to a table of contents.
360 o Reference: [W3C.REC-html401-19991224]
362 o Relation Name: copyright
363 o Description: Refers to a copyright statement that applies to the
364 link's context.
366 o Reference: [W3C.REC-html401-19991224]
368 o Relation Name: current
369 o Description: Refers to a resource containing the most recent
370 item(s) in a collection of resources.
371 o Reference: [RFC5005]
373 o Relation Name: describedby
374 o Description: Refers to a resource providing information about the
375 link's context.
376 o Documentation:
378 o Relation Name: edit
379 o Description: Refers to a resource that can be used to edit the
380 link's context.
381 o Reference: [RFC5023]
383 o Relation Name: edit-media
384 o Description: Refers to a resource that can be used to edit media
385 associated with the link's context.
386 o Reference: [RFC5023]
388 o Relation Name: enclosure
389 o Description: Identifies a related resource that is potentially
390 large and might require special handling.
391 o Reference: [RFC4287]
393 o Relation Name: first
394 o Description: An IRI that refers to the furthest preceding resource
395 in a series of resources.
396 o Reference:
398 o Relation Name: glossary
399 o Description: Refers to a glossary of terms.
400 o Reference: [W3C.REC-html401-19991224]
402 o Relation Name: help
403 o Description: Refers to a resource offering help (more information,
404 links to other sources information, etc.)
405 o Reference: [W3C.REC-html401-19991224]
407 o Relation Name: index
408 o Description: Refers to an index.
409 o Reference: [W3C.REC-html401-19991224]
411 o Relation Name: last
412 o Description: An IRI that refers to the furthest following resource
413 in a series of resources.
414 o Reference:
416 o Relation Name: license
417 o Description: Refers to a license associated with the link's
418 context.
419 o Reference: [RFC4946]
421 o Relation Name: next
422 o Description: Refers to the next resource in a ordered series of
423 resources.
424 o Reference: [W3C.REC-html401-19991224]
426 o Relation Name: next-archive
427 o Description: Refers to the immediately following archive resource.
428 o Reference: [RFC5005]
430 o Relation Name: payment
431 o Description: indicates a resource where payment is accepted.
432 o Reference:
433
435 o Relation Name: prev
436 o Description: Refers to the previous resource in an ordered series
437 of resources. Synonym for "previous".
438 o Reference: [W3C.REC-html401-19991224]
440 o Relation Name: previous
441 o Description: Refers to the previous resource in an ordered series
442 of resources. Synonym for "prev".
443 o Reference: [W3C.REC-html401-19991224]
445 o Relation Name: prev-archive
446 o Description: Refers to the immediately preceding archive resource.
447 o Reference: [RFC5005]
449 o Relation Name: related
450 o Description: Identifies a related resource.
451 o Reference: [RFC4287]
453 o Relation Name: replies
454 o Description: Identifies a resource that is a reply to the context
455 of the link.
456 o Reference: [RFC4685]
457 o Relation Name: section
458 o Description: Refers to a section in a collection of resources.
459 o Reference: [W3C.REC-html401-19991224]
461 o Relation Name: self
462 o Description: Conveys an identifier for the link's context.
463 o Reference: [RFC4287]
465 o Relation Name: start
466 o Description: Refers to the first resource in a collection of
467 resources.
468 o Reference: [W3C.REC-html401-19991224]
470 o Relation Name: stylesheet
471 o Description: Refers to an external style sheet.
472 o Reference: [W3C.REC-html401-19991224]
474 o Relation Name: subsection
475 o Description: Refers to a resource serving as a subsection in a
476 collection of resources.
477 o Reference: [W3C.REC-html401-19991224]
479 o Relation Name: via
480 o Description: Identifies a resource that is the source of the
481 information in the link's context.
482 o Reference: [RFC4287]
484 7. Security Considerations
486 The content of the Link header-field is not secure, private or
487 integrity-guaranteed, and due caution should be exercised when using
488 it.
490 Applications that take advantage of typed links should consider the
491 attack vectors opened by automatically following, trusting, or
492 otherwise using links gathered from HTTP headers. In particular,
493 Link headers that use the "anchor" parameter to associate a link's
494 context with another resource should be treated with due caution.
496 8. Internationalisation Considerations
498 Target IRIs may need to be converted to URIs in order to serialise
499 them in applications that do not support IRIs. This includes the
500 Link HTTP header.
502 Similarly, the anchor parameter of the Link header does not support
503 IRIs, and therefore IRIs must be converted to URIs before inclusion
504 there.
506 Relation types are defined as URIs, not IRIs, to aid in their
507 comparison. It is not expected that they will be displayed to end
508 users.
510 9. References
512 9.1. Normative References
514 [RFC2026] Bradner, S., "The Internet Standards Process -- Revision
515 3", BCP 9, RFC 2026, October 1996.
517 [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
518 Requirement Levels", BCP 14, RFC 2119, March 1997.
520 [RFC2231] Freed, N. and K. Moore, "MIME Parameter Value and Encoded
521 Word Extensions: Character Sets, Languages, and
522 Continuations", RFC 2231, November 1997.
524 [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
525 Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
526 Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
528 [RFC3864] Klyne, G., Nottingham, M., and J. Mogul, "Registration
529 Procedures for Message Header Fields", BCP 90, RFC 3864,
530 September 2004.
532 [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
533 Resource Identifier (URI): Generic Syntax", STD 66,
534 RFC 3986, January 2005.
536 [RFC3987] Duerst, M. and M. Suignard, "Internationalized Resource
537 Identifiers (IRIs)", RFC 3987, January 2005.
539 [RFC4288] Freed, N. and J. Klensin, "Media Type Specifications and
540 Registration Procedures", BCP 13, RFC 4288, December 2005.
542 [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
543 IANA Considerations Section in RFCs", BCP 26, RFC 5226,
544 May 2008.
546 9.2. Informative References
548 [RFC2068] Fielding, R., Gettys, J., Mogul, J., Nielsen, H., and T.
549 Berners-Lee, "Hypertext Transfer Protocol -- HTTP/1.1",
550 RFC 2068, January 1997.
552 [RFC4287] Nottingham, M. and R. Sayre, "The Atom Syndication
553 Format", RFC 4287, December 2005.
555 [RFC4685] Snell, J., "Atom Threading Extensions", RFC 4685,
556 September 2006.
558 [RFC4946] Snell, J., "Atom License Extension", RFC 4946, July 2007.
560 [RFC5005] Nottingham, M., "Feed Paging and Archiving", RFC 5005,
561 September 2007.
563 [RFC5023] Gregorio, J. and B. de hOra, "The Atom Publishing
564 Protocol", RFC 5023, October 2007.
566 [W3C.REC-html401-19991224]
567 Raggett, D., Hors, A., and I. Jacobs, "HTML 4.01
568 Specification", W3C REC REC-html401-19991224,
569 December 1999.
571 Appendix A. Notes on Using the Link Header with HTML4
573 HTML motivated the original syntax of the Link header, and many of
574 the design decisions in this document are driven by a desire to stay
575 compatible with these uses.
577 In HTML4, the link element can be mapped to links as specified here
578 by using the "href" attribute for the target URI, and "rel" to convey
579 both the relation type, as in the Link header. The context of the
580 link is the URI associated with the entire HTML document.
582 HTML4 also has a "rev" parameter for links that allows a link's
583 relation to be reversed. The Link header has a "rev" parameter to
584 allow the expression of these links in HTTP headers, but its use is
585 not encouraged, due to the confusion this mechanism causes as well as
586 conflicting interpretations among HTML versions.
588 All of the link relations defined by HTML4 have been included in the
589 link relation registry, so they can be used without modification.
590 However, extension link relations work differently in HTML4 and the
591 Link header; the former uses a document-wide "profile" URI to scope
592 the relations, while the latter allows the use of full URIs on
593 individual relations.
595 Therefore, when using the profile mechanism in HTML4, it is necessary
596 to map the profiled link relations to URIs when expressed in Link
597 headers. For example, in HTML:
599
600
601
602
603 [...]
605 could be represented as a header like this;
607 Link: ; rel="http://example.com/profile1/foo"
609 Profile authors should note this when creating profile URIs; it may
610 be desirable to use URIs that end in a delimiter (e.g., "/" or "#"),
611 to make extracting the specific relation in use easier.
613 Surveys of existing HTML content have shown that unregistered link
614 relation types that are not URIs are (perhaps inevitably) common.
615 Consuming HTML implementations should not consider such unregistered
616 short links to be errors, but rather relation types with a local
617 scope (i.e., their meaning is specific and perhaps private to that
618 document).
620 HTML4 also defines several attributes on links that are not
621 explicitly defined by the Link header. These attributes can be
622 serialised as link-extensions to maintain fidelity.
624 Appendix B. Notes on Using the Link Header with Atom
626 Atom conveys links in the atom:link element, with the "href"
627 attribute indicating the target IRI and the "rel" attribute
628 containing the relation type. The context of the link is either a
629 feed IRI or an entry ID, depending on where it appears; generally,
630 feed-level links are candidates for transmission as a Link header.
632 When serialising an atom:link into a Link header, it is necessary to
633 convert target IRIs (if used) to URIs.
635 Atom defines extension relation types in terms of IRIs. This
636 specification defines them as URIs, to aid in their comparison.
638 Atom allows registered link relation types to be serialised as
639 absolute URIs, because a base URI is defined for the registry. Such
640 relation types SHOULD be converted to the appropriate registered form
641 (e.g., "http://www.iana.org/assignments/relation/self" to "self") so
642 that they are not mistaken for extension relation types.
644 Note also that while the Link header allows multiple relations to be
645 associated with a single link, atom:link does not. In this case, a
646 single link-value may map to several atom:link elements.
648 As with HTML, atom:link defines some attributes that are not
649 explicitly mirrored in the Link header syntax, but they may also be
650 used as link-extensions.
652 Appendix C. Acknowledgements
654 This specification lifts the idea and definition for the Link header
655 from RFC2068; credit for it belongs entirely to the authors of and
656 contributors to that document. The link relation registrations
657 themselves are sourced from several documents; see the applicable
658 references.
660 The author would like to thank the many people who commented upon,
661 encouraged and gave feedback to this draft, especially including
662 Frank Ellermann, Roy Fielding and Julian Reschke.
664 Appendix D. Document history
666 [[ to be removed by the RFC editor before publication as an RFC. ]]
668 -04
670 o Defined context as a resource, rather than a representation.
671 o Removed concept of link directionality; relegated to a deprecated
672 Link header extension.
673 o Relation types split into registered (non-URI) and extension
674 (URI).
675 o Changed wording around finding URIs for registered relation types.
676 o Changed target and context URIs to IRIs (but not extension
677 relation types).
678 o Add RFC2231 encoding for title parameter, explicit BNF for title*.
679 o Add i18n considerations.
680 o Specify how to compare relation types.
681 o Changed registration procedure to Designated Expert.
682 o Softened language around presence of relations in the registry.
683 o Added describedby relation.
684 o Re-added 'anchor' parameter, along with security consideration for
685 third-party anchors.
687 o Softened language around HTML4 attributes that aren't directly
688 accommodated.
689 o Various tweaks to abstract, introduction and examples.
691 -03
693 o Inverted focus from Link headers to link relations.
694 o Specified was a link relation type is.
695 o Based on discussion, re-added 'rev'.
696 o Changed IESG Approval to IETF Consensus for relation registrations
697 (i.e., require a document).
698 o Updated RFC2434 reference to RFC5226.
699 o Registered relations SHOULD conform to sgml-name.
700 o Cautioned against confusing relation types with media types.
702 -02
704 o Dropped XLink language.
705 o Removed 'made' example.
706 o Removed 'rev'. Can still be used as an extension.
707 o Added HTML reference to introduction.
708 o Required relationship values that have a ; or , to be quoted.
709 o Changed base URI for relation values.
710 o Noted registry location.
711 o Added advisory text about HTML profile URIs.
712 o Disallowed registration of relations that only differ in case.
713 o Clarified language about IRIs in Atom.
714 o Added descriptions for 'first', 'last', and 'payment', referring
715 to current IANA registry entries, as these were sourced from
716 e-mail. Will this cause self-referential implosion?
717 o Explicitly updates RFC4287.
718 o Added 'type' parameter.
719 o Removed unnecessary advice about non-HTML relations in HTML
720 section.
722 -01
724 o Changed syntax of link-relation to one or more URI; dropped
725 Profile.
726 o Dropped anchor parameter; can still be an extension.
727 o Removed Link-Template header; can be specified by templates spec
728 or elsewhere.
729 o Straw-man for link relation registry.
731 -00
732 o Initial draft; normative text lifted from RFC2068.
734 Author's Address
736 Mark Nottingham
738 Email: mnot@mnot.net
739 URI: http://www.mnot.net/