> I think people have forgotten the explicit reference Roger 
> made to schematron, since schematron is a validation 
> technology that can be implemented in XSL-T it follows that 
> the expression matches(flt:Aircraft/flt:Altitude, '[0-9]+')  
> would give you the same capabilities as XML Schema datatype 
> checking in any actually useful scenario.

I think you're missing the point that schema-aware processing does much more
than run-time input validation. For example, it gives you compile time error
messages if you use the wrong kind of argument to a function or operator.
See my article http://www.stylusstudio.com/schema_aware.html for background
and some examples. You really have to try it out to develop a real complex
stylesheet to see the benefits - it's remarkable how much faster you can
find your bugs. Honest.

Michael Kay
http://www.saxonica.com/