1. Relax NG schema fragments are generated by an XSLT transform
2. ... and progressively flattened and simplified by a further set of XSLT transforms
3. DTDs, compact Relax NG, and W3C Schema are all generated using James Clark's trang (but not necessarily from the same inputs)

Vocabularies like MathML and SVG inclusion are managed by simply <include>ing the relevant RelaxNG grammars, each in their own namespace.