Weird file name side effect in validating.

Greetings,
     The attached tiny file validates as xml (which was expected).  If,
however, the same file is accidentally renamed as ch2-ex1.html then it does
not validate corresctly.  This is, to my way of thinking, ridiculous. 
Validtion should be the same irrespective of the file name!

               Regards,

                         Keith Hopper

-- 
Keith Hopper
Senior Lecturer
Department of Computer Science