A decomposition of XHTML 1.0 into a collection of
abstract modules that provide specific types of functionality -
allow subsets, extenstions, combination with other XML vocabularies
Also defines a way to develop your own modules that can be combined
with XHTML modules
Modularization of
XHTML became a Recommendation on 10 April 2001 including DTD
implementation,
Modularization of XHTML
in XML Schema is in progress (Last Call soon)