Override the default value for an attribute in the base type

Question

I have an existing type like this one that relates to the library level XSD:

<xs:complexType name="mybase"> <xs:attribute name="myattr" type="xs:string" default="123"/> </xs:complexType> 

And later, it is expanded with a number of more specific XSDs that implement specific application configuration requirements:

  <xs:element name="appconfig"> <xs:complexType> <xs:complexContent> <xs:extension base="mybase"> <xs:attribute name="specific_attr" type="xs:string" use="required"/> <!-- etc, more specific requirements --> </xs:extension> </xs:complexContent> </xs:complexType> </xs:element> 

We use this everywhere, but just run through the use case where for a particular application we want to use a different default value for "myattr". I poked various XSD docs but didn't find anything that could do this, is this possible?