There are four types of links available in DocBook: <link>, <ulink>, <olink>, and <xref>; we use all of them except olink.

Using Link for hypertext

The Link element is used to insert hypertext links in HTML and PDF. A Link has to have a target somewhere in the document or an included document. For example, this markup:

See <link linkend="pd-whitepapers">White Papers</link> and ... 

is rendered as: "See White Papers and ..." , and jumps to this target:

<sect1 id="pd-whitepapers">
  <title>White Papers</title>
  <para>The Cogent White Papers are ...</para>
</sect1>

This is the kind of link we use the most. It allows you to write any text you like within the tags. That text becomes the link, and any links that are invalid for any reason will still appear in the output as plain text. For this reason, we always use this link to link between books within the bookset, since any links between books are broken in the single-book PDF output.

Using Xref within a single document

If you want to link within a single document, you can use xref. This is an empty tag that gets automatically replaced with the title of the section or chapter you are linking to, when the document is processed. For example, this markup:

<xref linkend="pd-whitepapers">

is rendered as: " Section 5.6, “White Papers” " in HTML output, and goes to the same target as the link above.

Using Ulink for URLs

To link to URLs outside the document, use Ulink. For example:

<ulink url="http://www.jclark.com/jade/">Jade - James' DSSSL Engine</ulink> has information ...