Applying default values of type QName (and NOTATION)

When a default/fixed attribute/element value is of type QName/NOTATION, 
how is it applied to the instance? For example: 

<attribute name="att" type="QName" xmlns:p1="my_uri" default="p1:local"/>

If the above attribute doesn't appear in an instance, we should add a new 
attribute. But what would be the (string) value of the added attribute? 
(Note that the prefix "p1" might not be declared in the instance, or it's 
possible to be bound to a different namespace uri.) 

Thanks,
Sandy Gao
Software Developer, IBM Canada
(1-905) 413-3255
sandygao@ca.ibm.com