Schematron. An XML schema that is used to validate an XML document. Unlike grammar-based schema languages, Schematron is made up of XPath patterns that define the tree structures and relationships. It can be used by itself or embedded within a W3C XML Schema or RELAX NG schema. The final draft of an ISO version of Schematron was made available in late 2004 and was published as an ISO standard in 2006. For more information, visit www.schematron.com. See XML schema.