     <li><strong><a href="http://www.schematron.com/">Schematron</a></strong> - a rules-based XML schema
                language. Whereas DTD, WXS, and RNG are designed to express the structure of a content model,
                Schematron is designed to enforce individual rules that are difficult or impossible to express
                with other schema languages. Schematron is intended to supplement a schema written in
                structural schema language such as the aforementioned. Schematron is