HTML 4.0 Specification

HTML 4.0 Specification
Proposed Relationship Values
Status
The authorship of this document is unknown. It has no status.
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.
Browser-defined Links
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.
RESERVED. Defined by the user (using the WWW_HOME
environment variable). This relationship may not be overridden;
HTML user agents should ignore any author-supplied
REL=HOME setting.
BACK
RESERVED. Defined by the browser. This relationship may
not be overridden; HTML user agents should ignore any author-supplied
REL=BACK setting.
FORWARD
RESERVED. Defined by the browser. This relationship may
not be overridden; HTML user agents should ignore any author-supplied REL=FORWARD
setting.
Navigational Node Links
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.
NEXT
When REL=NEXT, the target document is the next document
in a sequence the author suggests the reader will find useful.
PREVIOUS
When REL=PREVIOUS, the target document is the previous document
in a sequence the author suggests the reader will find useful.
This is the inverse relationship to REL=NEXT, i.e. REV=NEXT
states the same thing as REL=PREVIOUS, similarly, REV=PREVIOUS
states the same thing as REL=NEXT.
CONTENTS
When REL=CONTENTS, the target is a table of contents that
includes the current document.
INDEX
When REL=INDEX, the target document acts as an index covering
the current document.
NAVIGATE
When REL=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.
COLLECTION
When REL=COLLECTION, the target document is an COLLECTION
that contains the current document.
When REV=COLLECTION, the current document is a COLLECTION
for the referenced document or object.
Hierarchy Links
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.
CHILD
The CHILD relationship identifies a subordinate or
subdocument. Any document may have multiple CHILD documents
within the same hierarchy.
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.
PARENT
The PARENT relationship identifies the superior or
container node.
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.
SIBLING
The SIBLING relationship identifies a sibling in the
current hierarchy. Any document may have multiple SIBLING documents
within the same hierarchy.
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.
TOP or ORIGIN
The TOP relationship identifies the logical top of a
hierarchical tree of which the current document is a
branch. BEGIN is a functional equivalent to TOP, if only
one of these values is specified.
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.
Sequence Links
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.
BEGIN or FIRST
The BEGIN relationship identifies the author-defined
start of a sequence of documents of which the current document is
a node. TOP is a functional equivalent to BEGIN when only
one of these values is specified.
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.
END or LAST
The END relationship identifies the author-defined end of
a sequence of documents of which the current document is a node.
TOP is a functional equivalent to END when only one is
specified.
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.
NEXT
The NEXT relationship identifies the next document in an
author-defined sequence of documents, such as a linear book.
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.
PREVIOUS or PREV
The PREVIOUS relationship identifies the previous
document in an author-defined sequence of documents, such
as a linear book.
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.
Related Documents
BIBLIOENTRY
The BIBLIOENTRY relationship identifies a bibliographic
entry.
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.

As We May Think
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.
BIBLIOGRAPHY
The BIBLIOGRAPHY relationship identifies a bibliography.
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.
CITATION
The CITATION relationship identifies a bibliographic
citation.
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
[1]
...
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

The HyperText Markup Language
...
DEFINITION
The DEFINITION relationship identifies a definition of a
term.
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.
HTTP
FOOTNOTE
The FOOTNOTE relationship identifies a footnote.
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.
GLOSSARY
The GLOSSARY relationship identifies a glossary.
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.
Meta Relationships
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.
MADE
The REV=MADE relationship has been used to identify the
author or "maker" of an HTML document. Typical HREF
values include a mailto: URI or the URL of the author's home page.
Author
AUTHOR
The AUTHOR relationship identifies a hypertext link to an
author.
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:
).
The COPYRIGHT relationship identifies a hypertext link to
a copyright notice.
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:


Copyright 1995 by Murray C. Maloney
DISCLAIMER
The DISCLAIMER relationship identifies a hypertext link
to a legal disclaimer. Usage is expected to be similar to that of
the COPYRIGHT hypertext link. As with the copyright
notice, there is no intention or expectation that such a link would
be the only way to express a disclaimer.
EDITOR
The EDITOR relationship identifies a hypertext link to an
editor. Usage is expected to be similar to that of the AUTHOR
hypertext link.
META
The META relationship identifies a hypertext link to a
node which contains meta-information related to the
current document. This is intended to be a generalized
meta-data relationship descriptor.
PUBLISHER
The PUBLISHER relationship identifies a hypertext link to
a publisher. Usage is expected to be similar to that of
the AUTHOR hypertext link.
TRADEMARK
The TRADEMARK relationship identifies a hypertext link to
a trademark notice. Usage is expected to be similar to that
of the COPYRIGHT hypertext link.
Other REL and REV Values Under Discussion
There are additional values for use with REL and REV that are
currently under discussion.
POINTER
The pointer relationship identifies a hypertext pointer.
That is, this is a way to do indirection in HTML.
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.

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.
STYLESHEET
The STYLESHEET relationship identifies a stylesheet.
When REL=STYLESHEET, the target document is a stylesheet
that may be applied to the current document. See
WD-style
for further information.
TRANSLATION
The TRANSLATION relationship specifies a translation to
another language.
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.
URC
The URC relationship identifies a Universal Resource
Citation. This is a proposed format for meta information
being developed within the IETF.