Schematron reference at Zvon
A complete reference for Schematron with examples.
Schematron Specification
A tree-pattern schema language, assertion-based rather than grammar-based, built on top of XSLT with XPath.
Schematron Tutorial at Zvon
A tutorial for Schematron with many examples.
Topologi Schematron Validator
Shareware that validates XML documents using Schematron, DTDs, and W3C XML Schemas