This lists all the proposed relationship values known by W3C at the time of writing. Some values have been dropped because they have been consistently misunderstood or because other equivalent mechanisms have been developed in the interim.
Some keywords are reserved and should not be used as REL/REV values.
HTML user agents typically provide a mechanism for navigating through the recent history of a user's access to documents; traditionally these operations are referred to as "back" and "forward". These mechanisms allow a user to step back through the documents which led to the current location and then forward again to retrace the path. Additionally, most user agents provide a mechanism to immediately return to a user-defined location, traditionally referred to as the home page, or "home". Since these browser actions are internally implemented by the browser, REL/REV keywords associated with these relationships are disallowed.
Navigational nodes are commonly used document objects which are designed by authors to assist the user in navigating through a closed or extended document set. The most familiar and common form of navigational node is a table of contents, which is a well known publishing device used for enumerating and ordering the contents of a closed document set.
When REV=COLLECTION, the current document is a COLLECTION for the referenced document or object.
It is quite common for documents to be developed or defined using a hierarchical model, or tree-like structure. The keywords listed below may be used within HTML documents to identify the hierarchical relationship of closely related nodes, such as the immediate parent, siblings and children. In addition, the TOP keyword may be used to identify the logical top (or root, depending on your perspective) of a hierarchical or tree-like structure.
The entire set of relationships may be used by a user agent to build a map of the hierarchical structure(s) of which the current document is a node. Hypertext links to documents identified with PARENT and TOP values are more likely to be accessible through an icon or other mechanism than documents identified with CHILD or SIBLING.
When REL=CHILD, the target document is a hierarchical child, or subdocument, of the current document.
When REV=CHILD, the current document is the hierarchical child, or subdocument, of the target.
When REL=PARENT, the target document is the hierarchical parent, or container, of the current document.
When REV=PARENT, the current document is the hierarchical parent, or container, of the target.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
When REL=SIBLING, the target document is a child of a common parent, or a hierarchical peer of the current document.
When REV=SIBLING, the current document is a child of a common parent, or a hierarchical peer of the target document.
When REL=TOP, the
target document is the logical top node of the tree.
When REV=TOP, the current document is the logical top of
the tree.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
NOTE: ORIGIN has been suggested as an alternative to TOP to provide metaphorical consistency with PARENT/CHILD/SIBLING. Comments are encouraged.
Given a set of documents, it is possible and often desirable to specify linear sequences to navigate through the set. A book, for example, is often organized as a linear sequence. With sequence links in each document, a user agent can step through or gather an entire book programmatically.
When REL=BEGIN, the
target document is the beginning of the sequence.
When REV=BEGIN, the current document is the beginning of
the sequence.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
When REL=END, the target document is the
end of the sequence.
When REV=END, the current document is the end of the
sequence.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
When
REL=NEXT, the target document is next after the current
document.
When REV=NEXT, the current document is next after the
target.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
When REL=PREVIOUS, the target document is previous to the current document.
When REV=PREVIOUS, the current document is previous to the target.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
BIBLIOENTRY would most typically be specified on an A element, as it would specify a hypertext link between a citation and a bibliographic entry describing the citation.
<A REL=BIBLIOENTRY HREF="biblio.html#V.Bush">
<CITE> As We May Think </CITE> </A>
The resource identified by this link may take any form desired by the author/publisher. A bibliographic entry may be presented in the style of a paper-based bibliographic entry, or it may be presented as the result of a database query.
The resource identified by this link may take any form desired by the author/publisher. A bibliography may be presented as an HTML document which is organized and presented in a style reminiscent of a paper-based bibliography. A bibliography may also be presented as a form-based query into a bibliographic database.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present a labeled icon in a tool bar.
When REL=CITATION, the target is a bibliographic citation. The anchor, in this case, may be a bibliographic entry. The anchor may also be a reference, thus allowing the reader a way to locate the citation:
... as described by Tim Berners-Lee
<A REL=CITATION HREF=#TBL> [1] </A>
...
When REV=CITATION, the anchor is a citation. Typically, the anchor would also be enclosed within a CITE element as shown in the example below. The example shown here also corresponds to the previous example, serving as its target by use of the NAME attribute.
... is described in Tim Berners-Lee's
<CITE><A NAME=TBL REV=CITATION HREF=./biblio/TBL >
The HyperText Markup Language </A> </CITE>
...
Definitions may be, but are not necessarily, contained within a glossary. DEFINITION would most typically be specified on an A element, as it would specify a hypertext link from a term to its definition.
<A REL=DEFINITION HREF="glossary.html#HTTP"> HTTP </A>
When REL=FOOTNOTE is specified on an A element, the anchor is a footnote marker and the target is a footnote. This can be used to link from the footnote marker (or a highlighted word, phrase, etc.) to an HTML document which contains the footnote text, or to a portion of the same document (see REV=FOOTNOTE).
When REL=FOOTNOTE is specified on a LINK element, it can specify a hypertext link to a set of footnotes which are related to the current document, or to a set of end-notes.
When REV=FOOTNOTE is specified on an A element, the anchor is a footnote; that is, the actual content of the footnote, as opposed to a footnote marker. In this case, the target specified by the HREF value, if any, is the footnote marker.
It has been suggested that the combination of REV=FOOTNOTE and NAME=... on an A element may be used to imply that the enclosed content not be rendered until a link to it is explicitly traversed, at which time it can be presented in a popup window. This would allow for the inclusion of footnote text within a document that would not be visible until the reader wanted it to be presented. Developers of user agents are free to experiment with this proposed feature, but there is no requirement that it be implemented.
When
REL=GLOSSARY, the target document is a glossary.
When REV=GLOSSARY, the current document is a glossary.
If the hypertext link is specified with REL in a LINK element, an HTML user agent may present an icon in a tool bar.
A glossary may be directly presented as an HTML document which is organized and presented in a style reminiscent of a paper-based glossary.
A glossary may also be accessed through an intermediary query mechanism. For example, the user highlights a word or phrase and presses the glossary button, thereby accessing the linked object and passing the highlighted text as an argument. The server returns the glossary entry relevant to the highlighted word.
There are classes of information which are not intrinsic to a document, but for which a clear and unambiguous association is often useful or even necessary. This section defines a small set of keywords which are related to ownership and legal notices.
Any attempt to rigorously define a closed set of meta-data classes, types, and formats is doomed to failure, partly due to the need for ongoing experimentation. Hence, the META keyword may be used to identify meta documents which do not necessarily have a clear or unambiguous definition. The content of the target node may be as specific format as a MARC record or an FGDC record, or it may be an author-defined format.
For each of the relationship keywords listed in this section, if the relationship is specified with REL in a LINK element, an HTML user agent may present a labeled icon in a tool bar.
<A REV=MADE HREF="mailto:murray@sq.com" > Author </A>
The hypertext link may be to the author's home page, a biography, an audio or video clip, or an agent which sends mail to the author (i.e., using mailto: ).
While it is arguable whether a copyright notice is required in every HTML file to assert copyright protection on it, there is clearly a desire to express copyright notice among a sufficient portion of the user community to justify support.
A basic copyright notice for this document may simply state: "Copyright 1995 by Murray C. Maloney". It may be desirable, in place of or in addition to such a notice, to have a hypertext link between each HTML document in a set and a single copyright notice, as in the following examples:
<LINK REL=COPYRIGHT HREF="copyright.html">
<A REL=COPYRIGHT HREF="copyright.html">
Copyright 1995 by Murray C. Maloney </A>
There are additional values for use with REL and REV that are currently under discussion.
When REV=POINTER, the anchor is a pointer to the target document. When a hypertext link is traversed to a LINK or A element with REV=POINTER, the target specified by the HREF value should be traversed, and so on, until a target without REV=POINTER is retrieved.
<LINK NAME=PSEUDO REV=POINTER HREF="real.html">
When REL=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.
When REL=STYLESHEET, the target document is a stylesheet that may be applied to the current document. See WD-style for further information.
When REL=TRANSLATION, the target is a translation to another language. This value will most typically be used with the LINK element, in combination with specification of the target document's language as a LANG attribute value. Presumably, REL=TRANSLATION can be used with the A element to specify a translation of a document fragment, such as a phrase in a foreign language.
When REV=TRANSLATION, the current document, or document fragment, is a translation of the target.