If attribute default present, 'use' must be optional

Just curious...

why in XSD section 3.2.3 Constraints on XML Representations of Attribute 
Declarations, Schema Representation Constraint: Attribute Declaration 
Representation OK (http://www.w3.org/TR/xmlschema11-1/#sec-src-attdecl) does 
it say:

    2 If default and use are both present, use must have the ·actual value· 
optional

Why can't a schema designer choose to have a mandatory attribute with a 
default value?

Thanks,

Pete Cordell
Codalogic Ltd
Interface XML to C++ the easy way using C++ XML
data binding to convert XSD schemas to C++ classes.
Visit http://codalogic.com/lmx/ or http://www.xml2cpp.com
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