One-size-fits-all no longer holds. A cellphone can't offer the same experience as a desktop machine
XHTML is designed for subsetting and extending
XHTML Modules form indivisible units for this purpose
Initial set of modules derived from XHTML 1.0 (HTML4)
New stuff includes Ruby, DOM2 Events, XForms
Major application is for Television and Mobile domains
Modules make it easier to define new document types that mix XHTML with other tag sets for vector graphics, animation, multimedia, math and more.
XHTML modules are being formalized using XML 1.0 DTDs and XML Schemas