The xref and link elements can be used the same as in DocBook 4. The only difference is that in DocBook 5 the linkend value must match an xml:id attribute on another element instead of an id attribute.

The olink element can be used the same as in DocBook 4. The targetptr attribute can match on an xml:id value from a DocBook 5 document, or an id value from a DocBook 4 document. An olink database could contain documents from both versions, and olinks will work between them.

In DocBook 5, there is no ulink element. Its function is handled instead by an xlink:href attribute on another element such as link.

In DocBook 5, you can use many other elements beside xref and link as the starting point for a link. DocBook 5 supports the use of xlink attributes on many elements. Those attributes effectively let you link from any element to any other element, almost. See the section “Universal linking in DocBook 5” for complete information.