DocBook is an XML/SGML vocabulary particularly well suited to books and papers about computer hardware and software (though it is by no means limited to these applications).
The DocBook Technical Committee maintains the DocBook schema. DocBook is officially available as a Document Type Definition (DTD) for both XML and SGML. It is unofficially available in other forms as well.
Current version 4.2 (2002-11)
No official version before 4.0