[tei-council] Quick ODD question

[Martin Holmes]

How do you make an attribute from an existing class required on an 
element? For instance:

<elementSpec ident="foo" ns="http://www.example.com/ns">

   <attList>

     <attRef class="att.global" ident="xml:id"/>

   </attList>

</elementSpec>

Is there any way I can override the optional status of @xml:id in the 
global class, to make it required on the new foo element, or do I have 
to re-create it?

Cheers,
Martin