Simon - The reason for avoiding this approach was that the xml attributes that go with the MatchType in the ... <xs:sequence> <xs:element ref="xacml:AttributeDesignator"/> </xs:element ref="xacml:AttributeValue"/> </xs:sequence> part of the choice are not required for the ... <xs:element ref="AnyMatch"/> part of the choice. So, the part of the choice that requires attributes would need another element definition and another tag. I am happy to explore the options and implications. All the best. Tim. ----------------------------------------- Tim Moses Tel: 613.270.3183