DocBook.orgSupport for MathML in equations is provided through an extension module for the DocBook V4.x XML DTD. This extension combines the DocBook and MathML DTDs.
Putting MathML elements in equation contexts is part of the standard DocBook V5.0 distribution. Note, however, that the DocBook V5.0 schema does not validate the MathML. Users interested in support for validation of compound documents are encouraged to consider NVDL, part of ISO/IEC 19757 - DSDL Document Schema Definition Languages.