Why are IDType, MeasureType, and others not derived from SuperType?
The XML Structure Task Force found a bug in XMLSpy that prevented refinement to the simple content of a complex type by restricting an existing complex type with simple content. It was decided that, in deference to XMLSpy users, schemas that use this capacity of XML Schema will be avoided. Instead, when a type with simple content is derived from a type with no content, generate type as a root type, generating inherited properties of that type locally instead of using XML Schema type inheritance.
