existing-rel-values: Difference between revisions

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Revision as of 20:12, 7 August 2011

<entry-title> existing rel values </entry-title>

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  • Do not add rel values from obsolete/superceded proposals or drafts, instead add them to the table in the "dropped" section.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:

Keyword Effect on link Effect on a, area Brief description
(from the relevant specification where possible) 		Link to defining specification
acquaintance not allowed external relation the person represented by the current document considers the person represented by the referenced document to be an acquaintance XFN
alternate external resource external relation 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 allowed allowed Refers to a document serving as an appendix in a collection of documents. HTML4 link type
bookmark not allowed allowed 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 allowed allowed Refers to a document serving as a chapter in a collection of documents. HTML4 link type
child not allowed external relation the referenced person is a child of the person represented by the current document XFN
colleague not allowed external relation the referenced person is a colleague of the person represented by the current document XFN
contact not allowed external relation the person represented by the current document considers the person represented by the referenced document to be a contact XFN
contents allowed allowed 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 allowed allowed Refers to a copyright statement for the current document. HTML4 link type
co-resident not allowed external relation the referenced person lives in the same residence as the person represented by the current document XFN
co-worker not allowed external relation the referenced person is a co-worker of the person represented by the current document XFN
crush not allowed external relation this person considers the referenced person to be a crush (i.e. has a crush on the referenced person) XFN
date not allowed external relation this person considers the referenced person to be a date (i.e. is dating the referenced person) XFN
friend not allowed external relation the person represented by the current document considers the person represented by the referenced document to be a friend XFN
glossary allowed allowed Refers to a document providing a glossary of terms that pertain to the current document. HTML4 link type
help allowed allowed Refers to a document offering help (more information, links to other sources information, etc.) HTML4 link type
kin not allowed external relation the referenced person is part of the extended family of the person represented by the current document XFN
license allowed allowed …indicates that the [referenced document] is a license for the current page. rel-license
me external relation external relation the referenced document represents the same person as does the current document XFN
met not allowed external relation this person has met the referenced person XFN
muse not allowed external relation the referenced person inspires the person represented by the current document XFN
neighbor not allowed external relation the referenced person lives nearby the person represented by the current document XFN
next external relation external relation 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 external relation external relation 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 not allowed external relation the referenced person is a parent of the person represented by the current document XFN
prev external relation external relation Refers to the previous document in an ordered series of documents. Some user agents also support the synonym "Previous". HTML4 link type
previous external relation external relation Synonym of prev HTML4 link type
section allowed allowed Refers to a document serving as a section in a collection of documents. HTML4 link type
sibling not allowed external relation the referenced person is a sibling of the person represented by the current document XFN
spouse not allowed external relation the referenced person is a spouse of the person represented by the current document XFN
start allowed allowed 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 external resource not allowed 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 allowed allowed Refers to a document serving as a subsection in a collection of documents. HTML4 link type
sweetheart not allowed external relation this person considers the referenced person to be their sweetheart XFN
tag not allowed allowed …indicates that the [referenced document] is an author-designated "tag" (or keyword/subject) for the current page. rel-tag
toc allowed allowed Synonym of contents (from "Table Of Contents") HTML4 link type
transformation allowed allowed 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
demo allowed allowed 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)
pronunciation …indicates that the destination of the 'link' element is a document providing a pronunciation lexicon for speech-synthesis purposes. rel-pronunciation
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.

You may list new proposed rel values here, and even better if you can list and link to POSH uses in the wild.

rel value summary brainstormed in and usage in the wild
accessibility indicate[s] that the destination of that hyperlink contains accessibility information for the current page. blog post which itself uses the rel value in a <link> tag in the head of the document.
author indicate[s] that the destination of that hyperlink represents the author of the current page. Combines with rel-me to chain authorship information. Google has said it will index rel-Author in this blog post, with further discussion of the rel-me connection See also the HTML5 spec


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


longdesc Alternative to the img longdesc attribute, for use on visible links Google search for rel=longdesc in the wild shows many sources of proposals. Please edit this to list the earliest and perhaps most recent/comprehensive proposal. No known real world POSH usage in the wild yet.
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
status the referenced document represents the status (or source of status updates) for the author of this document blog post

more brainstorming

See also:

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: If a value is missing from this table, it may have either already been promoted by writing it up as a proposal, or demoted by being explicitly dropped. Please check the other tables first before adding to this table.

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

External sources:


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 see brainstorming above for suggested use by google unknown DevMo / HTML5
canonical To help search engines disambiguate the same page with multiple representations Google Google/Microsoft/Yahoo!, Ask Jeeves
comment … … WCLR
contribution … … WCLR
EditURI Location of the xml-rpc gateway for a Wordpress install that allows external programs to add, edit and delete posts. Used by "WordPress blog client" software for automating posting and updating blog content from your desktop. Seen in WordPress, e.g. [1]. Description stubbed in rel-edituri.
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) HTML5 WCLR/HTML5
kinetic-stylesheet Imports a KSS 'kinetic stylesheet' to bind dynamic behavior to elements Used in the Plone Content Management System …
lightbox Hook - Indicates that following the link will trigger a "lightbox" script (Allowed in link only) (Google search for rel=lightbox in the wild) …
prettyPhoto See also "lightbox" (Google search for rel="prettyphoto" in the wild) …
made … … LRdraft
meta … 1999 W3C RDF syntax REC FOAF
microsummary … … Microsummary, be aware of: microsummary issues
noreferrer indicates that no referrer information is to be leaked when following the link. HTML5 HTML5
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
user … … WCLR
via … … WCLR
wlwmanifest Used by "Windows Live Writer," a Microsoft blog client for automating posting and updating blog content from your desktop. Seen in WordPress, e.g. [5]. Probably used by other blog content management systems as well. …

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.


HTML5 link type extensions

The following values are registered as link type extensions per the requirements in the WHATWG HTML spec and the requirements in the W3C HTML5 spec.


Before you register a new value:

  • Please check the Formats table and DO NOT re-register rel values that are already there. Please note that the W3C HTML WG has made a Decision to drop index, up, first and last from the HTML5 spec itself.
  • Please check the Dropped table and DO NOT register values that are already there. If you believe a rel value was dropped from another specification without prejudice, please provide link/cite to explicit text/decision stating as such (e.g. merely post-poned, or perhaps expected to be spun-out into its spec) from the group developing that specification.

Note that entries in the Formats table and entries that are already in HTML5 as built-in keywords are also considered extensions with the "Ratified" status.

Please make sure that registrations added here have all the required data filled in including:

  • "Effect on link"
  • "Effect on a and area" and
  • a link to a spec that documents the keyword as an HTML rel keyword. (A spec that merely defines the file format of the link target but does not define the rel keyword for use in HTML is not the kind of spec that is being required here.)

Entries lacking any of the above required data will likely be removed.

Changes to this registry may not be reflected in validators in real time.

Keyword Effect on link Effect on a, area Brief description Link to specification Synonyms Status
apple-touch-icon External Resource Not allowed Specify a Webpage Icon for a “Web Clip”, or “touch icon”, for mobile devices (not limited to Apple devices). Apple's Safari Web Content Guide probably redundant with rel=icon proposed
apple-touch-icon-precomposed External Resource Not allowed Specify a Webpage Icon for a “Web Clip”, or “touch icon”, for mobile devices (not limited to Apple devices). Apple's Safari Web Content Guide probably redundant with rel=icon proposed
apple-touch-startup-image External Resource Not allowed Specify a splashscreen for Web apps on iOS Safari Apple's Safari Web Content Guide maybe redundant with rel=icon with the sizes attribute? proposed
canonical External Resource Not allowed Specifies the canonical URL for the current document in order to help avoid duplicate content. Canonical meta tag Canonicalization at Google Webmaster Central Microsoft Webmaster Center Yahoo! Search Blog proposed
dns-prefetch External Resource Not allowed Tells the browser to perform dns lookup for host names ahead of use. Mozilla documentation Google documentation proposed
index Hyperlink Hyperlink Refers to a document providing an index for the current document. HTML4 proposed
openid.delegate External Resource Not allowed When the page that contains the link is used as an OpenID indentifier, the relying party perform sOpenID 1.1 authentication with the link target as the identifier instead. OpenID Authentication 1.1 proposed
openid.server External Resource Not allowed The OpenID server for the relying party to contact for OpenID 1.1 authentication OpenID Authentication 1.1 proposed
openid2.local_id External Resource Not allowed When the page that contains the link is used as an OpenID indentifier, the relying party perform sOpenID 2.0 authentication with the link target as the identifier instead. OpenID Authentication 2.0 proposed
openid2.provider External Resource Not allowed The OpenID server for the relying party to contact for OpenID 2.0 authentication OpenID Authentication 2.0 proposed
p3pv1 External Resource Not allowed References a machine-readable privacy policy description in the P3P format P3P spec proposed
pgpkey External Resource Not allowed Associates a PGP key with a Web page so that the Web page URL can be used as the commenter's URL in PGP-signed blog comments and the blogging system receiving the comment can fetch the key and verify the signature as belonging to the owner of the URL. PGP-Signed Comments proposed
prerender External Resource Not allowed Prerenders the Web page targeted by the link including running it scripts. Chrome Prerendering proposed
profile External Resource Contextual External Resource indicate[s] that the destination of that hyperlink is a metadata profile (e.g. an XMDP profile) for the current page or portion thereof. See also xmdp-brainstorming. rel-profile proposed


service External Resource Not allowed Atom Publishing Protocol editing service autodiscovery. Documentation on the WHATWG wiki proposed
shortcut External Resource Not allowed Used as a companion for icon for compatibility with IE. Documentation on MSDN proposed
shortlink External Resource Not allowed Specifies the preferred shortened URL for the page. shortlink spec proposed
timesheet External Resource Not allowed Applies a timesheet to the document. non-normative section in the Timesheet spec proposed
widget External Resource External Resource Autodiscovery for W3C widgets non-normative section in the Widget packaging spec proposed
wlwmanifest External Resource Not allowed Windows Live Writer manifest autodiscovery documentation on MSDN proposed


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:

rel value summary
(from the relevant specification where possible))		 defining specification
self From http://www.ietf.org/rfc/rfc4287.txt :

The value "self" signifies that the IRI in the value of the href attribute identifies a resource equivalent to the containing element.

 Atom http://www.ietf.org/rfc/rfc4287.txt
in-reply-to See http://code.google.com/apis/youtube/2.0/developers_guide_protocol_comments.html YouTube + Atom
collection Refers to a resource which represents a collection of which the current resource is a member.

When used in the Maze+XML media type, the associated URI returns the available collection of mazes.

Maze+XML, Collection+JSON, OpenSearch


east Refers to a resource to the "east" of the current resource.

When used in the Maze+XML media type, the associated URI points to a neighboring cell resource to the east in the active maze.

Maze+XML
exit Refers to a resource that represents the exit or end of the current client actvity or process.

When used in the Maze+XML media type, the associated URI points to the final exit resource of the active maze.

Maze+XML


north Refers to a resource that is "north" of the current resource.

When used in the Maze+XML media type, the associated URI points to a neighboring cell resource to the north in the active maze.

Maze+XML
south Refers to a resource that is "south" of the current resource.

When used in the Maze+XML media type, the associated URI points to a neighboring cell resource to the south in the active maze.

Maze+XML
west Refers to a resource that is "west" of the current resource.

When used in the Maze+XML media type, the associated URI points to a neighboring cell resource to the west in the active maze.

Maze+XML
item The target IRI points to a resource that is a member of a collection represented by the context IRI. Collection+JSON
... ... ...

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.

In general, you SHOULD NOT use any dropped values.

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.

In particular:

  • if a rel value was in a draft and is missing (without explanation) from the final spec, or
  • if a rel value was in a previous version of and is missing (without explanation) from an update to the specification (even a draft update)

Then absent any other information or explanation, it is presumed that the group/editors working on that specification decided to explicitly drop it (either in development, or in the updated version) and thus it should be obsoleted (not re-registered).

If you wish to add them, please research why such values were omitted from latter specifications before doing so. If you do discover the reasoning, please add a short statement or link to thereof into the appropriate place in the following table.

If there is more data, e.g. a link to an email of discussion of the spec development that explains why the rel value was dropped, and it explicitly states, e.g. it was without prejudice, or merely post-poned, or perhaps expected to be spun-out into its spec (or some other explicit positive reason), then it makes to link/cite that explicit text as part of a proposal.

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
footnote the anchor is a footnote marker and the target is a footnote 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


urc identifies a Universal Resource Citation HTML4dropped unknown

dropped without prejudice

In one known instance (from HTML4 to HTML5), some rel values were in an earlier version of a specification (or a proposal) and were dropped from a latter (draft) version, and it was noted that these values were dropped with the intent that they could still be proposed in a registry and thus they explicitly were not deprecated or obsoleted. This section documents such values as separate from the dropped section.

In general, you SHOULD NOT use any dropped values.

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.

Rel values that were dropped without prejudice from a specification will be considered similar to new values that have never been specified.

If you know of additional rel values that were dropped without prejudice from an update to a specification, please cite a URL and quote from the group developing the specification that officially states from that group that the dropping of the values was done without prejudice, or equivalent statement (such as explicit allowance of external registration, proposal, and/or development).

This table serves a historical purpose. If you wish to propose a value from this table, please copy it and leave it in place.

Sources:

  • Several rel values were explicitly dropped from HTML5. Per: Issue 118 Decision (emphasis added):

    "The final proposal argues for the removal of some relation values, to wit, it suggests removal of index, up, first and last. It was pointed out in survey comments that these relations are already registered in the IANA link relation registry. Presumably, these relations could also be entered in whatever other registry or registries HTML5 adopts for this purpose.

    ...

    "Next Steps

    ...

    "Since the relations to be removed are already registered at the IANA link relation registry, no further action is needed to include them there. WG members are free to register or record these relations elsehwere [sic], as well."

rel value summary defining specification why dropped
first synonym for begin HTML4dropped - never in an official spec Explicitly dropped from HTML5 interim draft yet permitted for external registry
index Refers to a document providing an index for the current document. was in HTML4 Explicitly dropped from HTML5 interim draft yet permitted for external registry
last synonym for end HTML4dropped - never in an official spec Explicitly dropped from HTML5 interim draft yet permitted for external registry
up When the document forms part of a hierarchy, this link references the immediate parent of the current document. was in HTML3 - but dropped in HTML4 Explicitly dropped from HTML5 interim draft yet permitted for external registry

See related HTML5: Link types for existing HTML5 specified rel values.

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: [6].
    • 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.

addtional external research

Here are some additional historical references to the development or rel-values which may be useful when researching values, especially why specific values may have been proposed but abandoned.

previous attempts at documenting

There have been previous attempts at documenting known rel values, most of which fell out of date due to being dependent on a single author maintaining them. They're listed here purely for historical reasons, and are not sufficient to be references of their own (since they're just individual curations of other references)

related

copyright

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