XHTML Modules and Markup Languages — How to create XHTML Family modules and markup languages for fun and profit

http://www.w3.org/MarkUp/Guide/xhtml-m12n-tutorial/

XHTML Modularization provides a structure for the creation of new markup languages through the extension of the XHTML Core modules and the use of the XHTML Module Framework. In some instances, people will want to create complete, proprietary markup languages through these mechanisms. In other instances, people may wish to create new, reusable modules that will be used by their organization or by others in the definition of markup languages. In either case, the mechanics of the modules added and the markup language definition are the same. This document describes the manner in which such modules are defined, and the way in which modules should be combined to create new markup languages.