DocBook is a domain-specific XML vocabulary widely used for technical documentation. There are widely-available tools to convert documents between DocBook and a wide variety of other formats, including ODF (q.v.) and into PDF.

DocBook is a fairly large vocabulary, and uses the “element pool” concept described by Eve Maler and Jeanne El Andaloussi in Developing SGML DTDs to make authoring easier: a core set of element names are available pretty much everywhere.

Sometimes people criticize DocBook because the most common conversion to HTML does not produce elegant pages, but that is not a feature of DocBook itself, and when the conversion goes well, people do not realize the original format was DocBook.