RELAX NG
Eric van der Vlist
O'Reilly & Associates, 2004
ISBN 0-596-00421-4
http://books.xmlschemata.org/relaxng/
This presentation: http://www.cafeconleche.org/slides/sd2005west/relaxng/
RELAX NG Tutorial: http://www.oasis-open.org/committees/relax-ng/tutorial.html