Date: Oct. 25, 1999
Link: http://www.ascc.net/xml/resource/schematron/schematron.html
Source Author or Organization: Rick Jelliffe, Academia Sinica Computing Centre

The Schematron is an XML structural validation language that uses patterns in trees instead of being based on grammars. It was designed to be easily implemented on top of any XSLT-compliant processor, and is available with an error-browser, many example files, demos, and detailed instructions.