Extending a choice model group in the derived type

If I have a base type B with the following content mode
 
B = (x | y) 
 
is there a way to create a derived type D with content model
 
D = (x |y |z) 
 
 
 
I thought of extension but at best I can create 
 
D = (x|y) z 
 
Restriction similarly doesn't work. Perhaps there is some clever way to do this with substitution groups I haven't thought of. 

Received on Thursday, 22 August 2002 13:39:13 UTC