The LINK element defines document relationships. Any number of LINK elements may be contained in the HEAD of a document. Many browsers lack support for LINK, so authors should not depend on the browser making the links available to the user.
The REL and REV attributes define the nature of the relationship between the documents and the linked resource. REL defines a link relationship from the current document to the linked resource while REV defines a relationship in the opposite direction. For example,
<LINK REL=Glossary HREF="foo.html">
indicates that foo.html is a glossary for the current document while
<LINK REV=Subsection HREF="bar.html">
indicates that the current document is a subsection of bar.html. The value of the REL and REV attributes is a space-separated list of link types.
Commonly used relationships include the next or previous document in a sequence, the starting page in a collection of documents, a document with copyright information, and information about the author. A document could define these relationships as follows:
<LINK REL=Prev HREF="base.html" TITLE="BASE - Document Base URI">
<LINK REL=Next HREF="meta.html" TITLE="META - Metadata">
<LINK REL=Start HREF="../" TITLE="HTML 4.0 Reference">
<LINK REL=Copyright HREF="/copyright.html" TITLE="Copyright Notice">
<LINK REV=Made HREF="mailto:firstname.lastname@example.org" TITLE="HTML 4.0 Reference Feedback">
While the value of REL and REV is case-insensitive, the Lynx browser renders the relationship exactly as given by the author. Authors should therefore be consistent in their case, and may wish to capitalize the first letter while using lowercase for the rest.
Authors can also use the LINK element to apply an external style sheet. REL=StyleSheet specifies a persistent or preferred style while REL="Alternate StyleSheet" defines an alternate style. A persistent style is one that is always applied when style sheets are enabled. The absence of the TITLE attribute indicates a persistent style.
A preferred style is one that is automatically applied. The combination of REL=StyleSheet and a TITLE attribute specifies a preferred style. Authors cannot specify more than one preferred style.
An alternate style is indicated by REL="Alternate StyleSheet". The user could choose to replace the preferred style sheet with an alternate one, though current browsers generally lack the ability to choose alternate styles.
A single style may also be given through multiple style sheets:
<LINK REL=StyleSheet HREF="basics.css" TITLE="Contemporary" TYPE="text/css">
<LINK REL=StyleSheet HREF="tables.css" TITLE="Contemporary" TYPE="text/css">
<LINK REL=StyleSheet HREF="forms.css" TITLE="Contemporary" TYPE="text/css">
In this example, three style sheets are combined into one "Contemporary" style that is applied as a preferred style sheet. To combine multiple style sheets into a single style, each style sheet's LINK must use the same TITLE.
LINK's MEDIA attribute specifies the media for which the linked resource is designed. With REL=StyleSheet, this allows authors to restrict a style sheet to certain output devices, such as printers or aural browsers. The attribute's value is a comma-separated list of media descriptors. The following media descriptors are defined in HTML 4.0 and are case-sensitive:
Netscape Navigator 4.x incorrectly ignores any style sheet linked with a MEDIA value other than screen. For example, MEDIA="screen, projection" will cause the style sheet to be ignored by Navigator 4.x, even if the presentation device is a computer screen. Navigator 4.x also ignores style sheets declared with MEDIA=all. Most other browsers ignore the MEDIA attribute.
The optional HREFLANG and CHARSET attributes of LINK give the language and character encoding, respectively, of the link. The language should be specified according to RFC 1766; examples include en for English, en-US for American English, and ja for Japanese. Examples of character encodings include ISO-8859-1, SHIFT_JIS, and UTF-8.
The Alternate link relationship defines an alternate version of the document. Translations of a page can be identified by using REL=Alternate along with the HREFLANG attribute. Versions of the page tailored for specific media can be provided by combining REL=Alternate with the MEDIA attribute. Some examples follow:
<LINK REL=Alternate HREF="index.fr.html" HREFLANG=fr LANG=fr TITLE="Version française">
<LINK REL=Alternate HREF="index.ja.html" HREFLANG=ja CHARSET="SHIFT_JIS" TITLE="Japanese version">
<LINK REL=Alternate HREF="/distribution/html40.pdf" TYPE="application/pdf" MEDIA=print TITLE="PDF version">
Note that the LANG and DIR attributes apply to the text of the TITLE attribute, not to the content of the link.
The TARGET attribute is used with frames to specify in which frame the link should be rendered. If no frame with such a name exists, the link is rendered in a new window unless overridden by the user. Special frame names begin with an underscore:
In HTML 4.0, the TARGET attribute value is case-insensitive, so that _top and _TOP both have the same meaning. However, most browsers treat the TARGET attribute value as case-sensitive and do not recognize _TOP as having the special meaning of _top.