This command returns 0 on successful validation, 1 on an error:

xmllint --xinclude --noout --dtdvalid http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd <Topicfile>

It validates Docbook, but doesn't validate that a topic follows the schema that we need (ie: it is a section).

We can extend this test in the future, by using a customized DTD that will only validate a Docbook section as the root node.

In the short term, we need to validate each topic on build, and substitute the following for a failed topic:

<section>
  <title>Topic.Title</title>

  <xi:include href="Topic exists but failed validation notice"/>

  Topic.Description
</section>