In the following DocBook 4 document the content of the listitem element does not match the rules of the DocBook 4 schema, that is docbookx.dtd.
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.4//EN" "http://www.docbook.org/xml/4.4/docbookx.dtd"> <article> <title>Article Title</title> <sect1> <title>Section1 Title</title> <itemizedlist> <listitem> <link>a link here</link> </listitem> </itemizedlist> </sect1> </article>
The Validate Document action will return the following error:
Unexpected element "link". The content of the parent element type must match "(calloutlist|glosslist|bibliolist|itemizedlist|orderedlist|segmentedlist|simplelist |variablelist|caution|important|note|tip|warning|literallayout|programlisting |programlistingco|screen|screenco|screenshot|synopsis|cmdsynopsis|funcsynopsis |classsynopsis|fieldsynopsis|constructorsynopsis|destructorsynopsis|methodsynopsis |formalpara|para|simpara|address|blockquote|graphic|graphicco|mediaobject|mediaobjectco |informalequation|informalexample|informalfigure|informaltable|equation|example|figure |table|msgset|procedure|sidebar|qandaset|task|anchor|bridgehead|remark|highlights |abstract|authorblurb|epigraph|indexterm|beginpage)+".
This error message is a little more difficult to understand, so understanding of the syntax or processing rules for the DocBook XML DTD's listitem element is recommended. However, the error message does give us a clue as to the source of the problem, indicating that "The content of element type c must match".
Luckily most standards based DTD's, XML Schema's and Relax NG schemas are supplied with reference documentation. This enables us to lookup the element and read about it. In this case you should learn about the child elements of listitem and their nesting rules. Once you have correctly inserted the required child element and nested it in accordance with the XML rules, the document will become valid on the next validation test.