You can form links between a callout marker and its associated callout text. A co callout marker can take a linkends attribute (note the plural) to point to the callout element that contains its text. A callout elements can take an arearefs (not linkend) attribute to point back to its co element. See the section “Callouts” for more information.

If you are using area elements in programlistingco to attach callout markers to imported text, then you can put a linkends (note the plural) attribute on each area element. See the section “Callouts on imported text” for more information.

When doing callouts, sometimes more than one place in your example needs to point to the same callout description. To make sure they have the same callout bug number, use a coref element instead of another co element. See the section “Callouts” for more information.

If you are using a cmdsynopsis, you can break out parts of a complex command synopsis using synopfragment. You can insert a synopfragmentref with a linkend attribute to point to a synopfragment. See the reference page for synopfragment in DocBook: The Definitive Guide for an example.

Sometimes you need to make more than one reference to the same footnote. For example, you might have two places in your text where the explanation in a footnote is appropriate. Rather than create two identical footnote elements, one of them can be a footnoteref element. That is an empty element with a linkend attribute that points to the id you put in the footnote element.

You can link from your text into a glossary. An inline glossterm in a paragraph can have a linkend attribute that points to the id of a glossentry in a glossary. See the section “Linking to a glossary entry” for more information.