Schema.org markup in HTML, embedded as Microdata or RDFa 1.1 Lite, is used by the major search engines to optimise discovery of relevant information.
Schema.org has a proposed vocabulary for technical documentation: http://blog.schema.org/2012/06/newvocabularies-for-technical.html
Using that vocabulary it's possible to, for example, mark up code samples with the product that they are relevant to, the product component, and the programming language.
It looks like schema.org is converging on RDFa Lite:
Manu Sporny makes a solid case that RDFa Lite is the one to go with: http://manu.sporny.org/2012/mythical-differences/
This RFE is for Microdata or RDF 1.1 lite support in Docbook, so that we can use the Schema.org markup vocabularies in the HTML output from Docbook.