I'm not sure if I'm wright with my interpretation of clause 3 of derivation-ok-restriction. In special the following sentence:

"...and for every attribute information item A in E.[attributes], B's default binding for A subsumes that defined by T."

As I read it the following complex type is invalid:

<xs:complexType name="T">
   <xs:anyAttribute namespace="##any" processContents="skip"/>
</xs:complexType>

In this case the base type definition B would be xs:anyType and T would be the complex type T. The default binding for any potential attribute information item would be skip for T and lax for B (xs:anyType has a lax attribute wildcard). So B's default binding for A (lax) will not subsume T's default binding for A (skip).