An Introduction to RELAX NG
http://www.devarticles.com/c/a/XML/An-Introduction-to-RELAX-NG/

McCullough, Peyton
Dev Articles
2008

Abstract:

RELAX NG is not a capitalized misspelling of something you probably get to do all too rarely as a busy programmer and web designer. If you use XML to any great degree, you'll want to take a close look at it. It can help make your life as a web developer easier, allowing you to relax a little more.