The complexContent element of an XML Schema is used to create derived types that restrict or extend some base type. In instance documents, any location that expects the base type can contain any of the derived types.

This example is based on the international purchase order example in the XML Schema primer. The international purchase order schema has an Address type, and defines two derived types USAddress and UKAddress. Wherever an Address is expected in the instance document, a USAddress or a UKAddress can be substituted. This example demonstrates how HydraExpress handles this substitutability of types.

This example also illustrates the use of the XML Schema include feature.