Mark Birbeck wrote:

> >  I know I could use 
> > XInclude, XLink, XPointer, and any other XML libraries 
> > designed to extend XML-based languages.  I meant, are there 
> > any plans for the creation of schemas/DTD's that allow one to 
> > use XInclude within XHTML, without having to resort to either 
> > writing a custom schema or accepting that validation will not occur?
> 
> Indeed. I have actually looked at this, but not recently. It seems like it
> should be pretty easy to add the XInclude element to the XHTML
> Modularisation schemas. It's something we intend to add to the schemas we
> have created for our Sidewinder Web Applications Viewer (which in turn use
> the M12N schemas), but I haven't yet tackled it. The annoying thing is, now
> you have made me think of it, I am pretty sure that there is no "extend
> every element" mechanism in M12N. If there isn't, it may still be possible
> to add one, and if we can't do that, then we'll just have to do it the long
> way.

You might want to have a look at the thread starting from:

  Addressing the XInclude/Schema issue in RELAX NG?
  http://groups.yahoo.com/group/rng-users/message/353 

-- 
Masayasu Ishikawa / mimasa@w3.org
W3C - World Wide Web Consortium