existing-rel-values

existing rel values

This page contains tables of known HTML rel values from specifications, formats, proposals, brainstorms, and non-trivial POSH usage in the wild. In addition, dropped and rejected values are listed at the end for comprehensiveness.

usage: see how is 'rel' used. Regarding rev, see: should 'rev' even be used.

formats

These rel values are defined formats from specifications (HTML 4, microformats) are thus are recommended for general use. Alphabetically ordered by value.

Note:

• Do not add rel values you find in the wild to this table of rel formats, instead add them to the table in the POSH section.
• Do not add non-HTML rel values you find to this table of rel formats, instead add them to the table in the non HTML rel values section.
• Do not add rel values from obsolete/superceded proposals or drafts, instead add them to the table in the "dropped" section.

Sources:

• W3C HTML 4 link type and GRDDL specs.
• xfn and other microformats

rel value	summary (from the relevant specification where possible))	defining specification
acquaintance	the person represented by the current document considers the person represented by the referenced document to be an acquaintance	XFN
alternate	Designates substitute versions for the document in which the link occurs. When used together with the lang attribute, it implies a translated version of the document. When used together with the media attribute, it implies a version designed for a different medium (or media).	HTML4 link type
appendix	Refers to a document serving as an appendix in a collection of documents.	HTML4 link type
bookmark	Refers to a bookmark. A bookmark is a link to a key entry point within an extended document. The title attribute may be used, for example, to label the bookmark. Note that several bookmarks may be defined in each document.	HTML4 link type
chapter	Refers to a document serving as a chapter in a collection of documents.	HTML4 link type
child	the referenced person is a child of the person represented by the current document	XFN
colleague	the referenced person is a colleague of the person represented by the current document	XFN
contact	the person represented by the current document considers the person represented by the referenced document to be a contact	XFN
contents	Refers to a document serving as a table of contents. Some user agents also support the synonym ToC (from "Table of Contents").	HTML4 link type
copyright	Refers to a copyright statement for the current document.	HTML4 link type
co-resident	the referenced person lives in the same residence as the person represented by the current document	XFN
co-worker	the referenced person is a co-worker of the person represented by the current document	XFN
crush	this person considers the referenced person to be a crush (i.e. has a crush on the referenced person)	XFN
date	this person considers the referenced person to be a date (i.e. is dating the referenced person)	XFN
friend	the person represented by the current document considers the person represented by the referenced document to be a friend	XFN
glossary	Refers to a document providing a glossary of terms that pertain to the current document.	HTML4 link type
help	Refers to a document offering help (more information, links to other sources information, etc.)	HTML4 link type
index	Refers to a document providing an index for the current document.	HTML4 link type
kin	the referenced person is part of the extended family of the person represented by the current document	XFN
license	…indicates that the [referenced document] is a license for the current page.	rel-license
me	the referenced document represents the same person as does the current document	XFN
met	this person has met the referenced person	XFN
muse	the referenced person inspires the person represented by the current document	XFN
neighbor	the referenced person lives nearby the person represented by the current document	XFN
next	Refers to the next document in a linear sequence of documents. User agents may choose to preload the "next" document, to reduce the perceived load time.	HTML4 link type
nofollow	indicates that the destination of that hyperlink SHOULD NOT be afforded any additional weight or ranking by user agents which perform link analysis upon web pages (e.g. search engines).	rel-nofollow
parent	the referenced person is a parent of the person represented by the current document	XFN
prev	Refers to the previous document in an ordered series of documents. Some user agents also support the synonym "Previous".	HTML4 link type
previous	Synonym of prev	HTML4 link type
section	Refers to a document serving as a section in a collection of documents.	HTML4 link type
sibling	the referenced person is a sibling of the person represented by the current document	XFN
spouse	the referenced person is a spouse of the person represented by the current document	XFN
start	Refers to the first document in a collection of documents. This link type tells search engines which document is considered by the author to be the starting point of the collection.	HTML4 link type
stylesheet	a style sheet for the current document used with the invisible <link href> element which is not ideal for content relationships. Content relationships should be user visible and thus uses with <a href> are strongly preferred. Unfortunately the use of stylesheet in user visible content like <a href> appears to be strictly theoretical.	HTML4 link type
subsection	Refers to a document serving as a subsection in a collection of documents.	HTML4 link type
sweetheart	this person considers the referenced person to be their sweetheart	XFN
tag	…indicates that the [referenced document] is an author-designated "tag" (or keyword/subject) for the current page.	rel-tag
toc	Synonym of contents (from "Table Of Contents")	HTML4 link type
transformation	Relates a source document to a transformation, usually represented in XSLT, that relates the source document syntax to the RDF graph syntax. Used in GRDDL	GRDDL spec

notes

• rel="alternate" can take further meaning from additional attributes, such as
  • rel="alternate" lang="fr" (French language version of this page)
  • rel="alternate" media="print" (printable version of this page)
  • rel="alternate" media="handheld" (version of the page intended or better for handheld/portable devices like PDAs, cell phones, etc.)

• Synonyms such as "previous", "toc" are not as widely supported as the main term.

proposals

A few rel values have been developed as drafts as a result of going through most of the microformats process, and are thus listed here for your serious consideration. You may use these values, and if you find any problems with them please point them out on the respective "issues" page for the rel value.

rel value	summary	proposed in	external spec (if any)
directory	…indicates that the destination of the hyperlink is a directory listing containing an entry for the current page.	rel-directory
enclosure	…indicates that the destination of that hyperlink is intended to be downloaded and cached.	rel-enclosure	RFC4287
home	…indicates that the [referenced document] is the homepage of the site in which the current page appears.	rel-home
payment	…	rel-payment

brainstorming

Several rel values are being brainstormed as potential microformats and are thus listed here. If you find you have a use for such semantics in real world examples, consider trying out these values and provide feedback on the respective brainstorming page(s) with your results and experiences.

rel value	summary	brainstormed in
accessibility	indicate[s] that the destination of that hyperlink contains accessibility information for the current page.	blog post
bibliography	indicate[s] that the destination of that hyperlink is a bibliography for the current page.	mailing list post, 2007-10-15
cite	indicate[s] that the destination of that hyperlink is an authoritative source or a precedent to the current page.	distributed-conversation-brainstorming
group	the referenced document represents a group to which the person represented by the current document belongs	group-brainstorming
map	Link to a map. Possibly embedded within an adr, hCard, geo or hCalendar. Parsers MAY attempt to parse the URL if it is a link to a known map site (e.g. Geohash, Google Maps, Multimap) and extract co-ordinates and other useful data.	(to TobyInk by email)
member	the referenced document represents a member of the group represented by the current document	group-brainstorming
product	…	product-brainstorming
profile	indicate[s] that the destination of that hyperlink is a metadata profile (e.g. an XMDP profile) for the current page or portion thereof	xmdp-brainstorming
shortlink	the referenced document represents the current document but with a shorter URL	blog post
vcalendar-parent	link from an event to a containing event	hCalendar 1.1 draft
vcalendar-child	link from an event to a contained event	hCalendar 1.1 draft
vcalendar-sibling	link from an event to a related event with the same container	hCalendar 1.1 draft

more brainstorming

See also:

• genealogy-brainstorming for some thoughts on possible additional values for family relationships (use existing XFN parent, child, sibling, spouse, kin values first though)
• xpn-brainstorming for some thoughts on possible additional values for professional relationships (use existing XFN co-worker, colleague values first though)

POSH usage

There are numerous rel values used as POSH, both in the wild, whose origins are not necessarily known, nor are their meanings consistent. There are also numerous rel values from external proposals of varying degrees of merit. It is useful to document their existence and summarize their implied meanings/usage intent as research that may be used to perhaps take one or more of them thru the microformats process if there is both sufficient interest and sufficient in the wild usage.

Note: this list is incomplete, please help complete it from the following sources:

External sources:

• Meta Information in DevMo Docs (DevMo)
• Microsummary
• Web Communication Link Relationships (WCLR)
• W3C Link Relationship values draft (LRdraft) - from a draft of the HTML spec circa 1991.
• HTML5 draft Liable to change
• FOAF Project Wiki: Autodiscovery (FOAF)
• RFC4685
• Google Blog

rel value	summary	origin	proposal(s)
archive	index of archived entries	unknown, perhaps Wordpress open source blogging software	WCLR
archives	Provides a link to a collection of records, documents, or other materials of historical interest.		HTML5
author	…	unknown	DevMo
canonical	To help search engines disambiguate the same page with multiple representations	Google	Google/Microsoft/Yahoo!, Ask Jeeves
comment	…	…	WCLR
contribution	…	…	WCLR
details	…	(seen on w3c.org news log in a "read more" permalink)	…
EditURI	…	Seen in WordPress, e.g. [1]	…
endorsed	…	…	WCLR
external	Indicates that the referenced document is not part of the same site as the current document.	…	HTML5
fan	xxxx.	…	hcard-user-profile-authoring
feed	Gives the address of a syndication feed for the current document.	…	WCLR/ HTML5
icon	Imports an icon to represent the current document. (Allowed in link only)	…	WCLR/ HTML5
lightbox	…	(Google search for rel=lightbox in the wild)	…
made	…	…	LRdraft
meta	…	1999 W3C RDF syntax REC	FOAF
microsummary	…	…	Microsummary, be aware of: microsummary issues
openid.delegate	…	(Google search for rel=openid.* in the wild)	…
openid.server	…	(Google search for rel=openid.* in the wild)	…
permalink	…	…	WCLR
pgpkey	(see also rel-publickey)	…	[2], [3]
pingback	Gives the address of the pingback server that handles pingbacks to the current document. (Allowed in link only)	…	WCLR/ HTML5
prefetch	Specifies that the target resource should be pre-emptively cached. (Allowed in link only)	…	HTML5
publickey	(see also rel-pgpkey)	…	[4]
referral	…	…	WCLR
related	…	…	WCLR
replies	indicates a continued thread	unknown	RFC4685
resource	…	…	WCLR
search	…	unknown	unknown
sidebar	Specifies that the referenced document, if retrieved, is intended to be shown in the browser's sidebar (if it has one).		HTML5
sponsor	…	…	WCLR
trackback	…	unknown, perhaps open source Movable Type blogging software	WCLR
unendorsed	(probably redundant to nofollow)	…	WCLR
up	Provides a link to a document giving the context for the current document.	…	HTML5
user	…	…	WCLR
via	…	…	WCLR

WCLR

The WCLR proposal is described by its author (in e-mail, 2007-09-25) as:

…now effectively obsolete, since HTML5 and Microformats cover all the worthwhile relationships in that already.

These are covered by HTML5 already:

• permalink -> bookmark
• archive -> archives
• feed
• pingback
• unendorsed -> nofollow

The rest now seem unnecessary.

Nonetheless, there may be some mileage in using them in microformats, at least until HTML5 is widely available.

non HTML rel values

There are markup languages other than HTML that also have a rel attribute, often based upon the HTML rel attribute. It is useful to document some of these other languages and their rel values for both reference purposes, and to provide background research for the possible development and re-use of these values in HTML, as poshformats or microformats

Sources:

• Atom RFC4287 specification.
• See http://www.iana.org/assignments/link-relations.html for more.

rel value	summary (from the relevant specification where possible))	defining specification
self	See http://www.rfc-editor.org/rfc/rfc4287.txt	Atom
...	...	...

dropped

The following rel values were in earlier version(s) of specification(s) and it is presumed by their absence from the most recent version of the respective specification(s) that they have been deprecated or obsoleted. Use of them could be considered a bit more standard than just POSH, although you may wish to research why such values were omitted from latter specifications before using them. If you do discover the reasoning, please add a short statement or link to thereof into the appropriate place in the following table.

In general, you SHOULD NOT use any dropped values.

In addition, if any such values have been superceded by standard values (see the first table on this page), then you MUST NOT use the dropped versions.

Sources:

• HTML3 (HTML3) - has been superceded by HTML 3.2 - which itself has been superceded by HTML 4.0 - which itself has been updated by HTML 4.01, commonly referred to as "HTML 4" in this wiki and other places.)
• Proposed HTML 4.0 link types (HTML4dropped) - obsoleted/superceded by the HTML 4.0 Recommendation. Any values that were in the "Proposed HTML 4.0 link types" document but didn't make it into the HTML 4.0 Recommendation were thus explicitly dropped and should be avoided.

rel value	summary	defining specification	why dropped
banner	Was used to reference another document to be used as banner for this document (i.e. a form of "include" statement).	HTML3	unknown
begin	identifies the author-defined start of a sequence of documents of which the current document is a node.	HTML4dropped	unknown
biblioentry	identifies a bibliographic entry	HTML4dropped	unknown
bibliography	identifies a bibliography	HTML4dropped	unknown
child (obsolete/superceded)	the target document is a hierarchical child, or subdocument, of the current document	HTML4dropped	unknown
citation	the target is a bibliographic citation	HTML4dropped	unknown
collection	the target document is an collection that contains the current document	HTML4dropped	unknown
definition	identifies a definition of a term	HTML4dropped	unknown
disclaimer	identifies a hypertext link to a legal disclaimer	HTML4dropped	unknown
editor	identifies a hypertext link to an editor	HTML4dropped	unknown
end	identifies the author-defined end of a sequence of documents of which the current document is a node.	HTML4dropped	unknown
first	synonym for begin	HTML4dropped	unknown
footnote	the anchor is a footnote marker and the target is a footnote	HTML4dropped	unknown
last	synonym for end	HTML4dropped	unknown
navigate	the target document contains information such as a image map that will help users to gain a sense of how and where to found information	HTML4dropped	unknown
origin	synonym for top	HTML4dropped	unknown
parent (obsolete/superceded)	the target document is the hierarchical parent, or container, of the current document	HTML4dropped	unknown
pointer	the target is a pointer to the real target. This value can be used by a user agent to perform a pre-fetch of the specified target for evaluation until the real target is reached	HTML4dropped	unknown
publisher	identifies a hypertext link to a publisher	HTML4dropped	unknown
sibling (obsolete/superceded)	the target document is a child of a common parent, or a hierarchical peer of the current document	HTML4dropped	unknown
top	the target document is the logical top node of the tree (see also begin)	HTML4dropped	unknown
trademark	identifies a hypertext link to a trademark notice	HTML4dropped	unknown
translation	the target is a translation to another language	HTML4dropped	unknown
up	When the document forms part of a hierarchy, this link references the immediate parent of the current document.	HTML3	unknown, but proposed for re-introduction in HTML5
urc	identifies a Universal Resource Citation	HTML4dropped	unknown

rejected

Some rel values have been proposed and rejected. They are listed here to make that explicit. Authors MUST NOT use rejected rel values.

Source: rejected-formats.

rel value	origin / proposal	why rejected
pavatar	pavatar	rejected-formats#Pavatar

unspecified

Some rel values have been added to this page perhaps in one of the tables above, but no examples, nor an actual specification explicitly stating that the value(s) should be used in the HTML4 'rel' attribute could be found. They are listed here in the hopes someone can discover more specific/precise URLs to examples or specifications about them (preferably both). Until such precise URLs to examples/specs are provided, the values can be treated as they are purely theoretical and thus of little interest.

rel value	summary	source
schema.DC	…	Dublin Core
schema.DCTERMS	…	Dublin Core

Notes:

• Dublin Core. This search may help: [5].
  • examples from that search only use invisible <link href> element. At first glance it appears the results from the search show only uses with the invisible <link href> element which is not ideal for content relationships. Content relationships should be user visible and thus uses with <a href> are strongly preferred.
    • RFC2731 defines rel="schema.AC" and rel="schema.RC" with the pattern rel="schema.PREFIX" as a syntax for defining namespaces for use in meta[@name], *[@rel], *[@rev] and (as per eRDF) *[@class] attributes. A link to a Dublin Core metadata schema is generally not suitable for end users, so <link href> appears to be more appropriate than <a href> for those that use Dublin Core metadata schemas.
  • proposal to use in content currently only theoretical. Thus unfortunately the use of Dublin Core in user visible content like <a href> appears to be strictly theoretical. See microformats-discuss/2008-January/011445.html for a proposal to use Dublin Core in user visible content.

tools

See implementations.

related

• rel
• existing rel values
• rel examples
• rel FAQ
• rel design pattern
• rel values issues
• rel-registry
• elemental-microformats
• existing-class-names