This is the home of the MathML 2.0 XML Schema from the MathML Working Group.

All the details needed to use it should be covered in appendix A of
MathML 2.0, 2nd edition

This schema is not normative. It is only provided as a tool to validate MathML
instances, without any guarantee on the accuracy of the results. This version
will be updated gradually to incorporate corrections or changes.