Flattened DocBook plus CSSa.
The unaltered DocBook Publishers V5.1CR1-1 RNG schema is included here (might have included DocBook as a submodule but didn’t find docbook.rng in its repo).
CSSa is included as a submodule from https://github.com/gimsieke/CSSa
git clone https://github.com/gimsieke/Hub hub
cd hub
git submodule init
git submodule update