v7.3 (January 06, 2016): Fully supports DocBook 5.1 —now an OASIS standardout of the box.

DocBook 5.1 assemblies are processed using free, open source, XMLmind Assembly Processor v1.0. Version 1.0 is the first version to fully support processing DocBook 5.1 assemblies. This includes XInclude 1.1, DocBook Transclusion and assembly features such as relationships and transforms .