<xs:element id="union" name="union" >
  <xs:complexType>
    <xs:annotation>
      <xs:documentation source="http://www.w3.org/TR/xmlschema-2/#element-union">
          memberTypes attribute must be non-empty or there must be
          at least one simpleType child
        </xs:documentation>
    </xs:annotation>
    <xs:complexContent mixed="false">
      <xs:extension base="xs:annotated">
        <xs:sequence>
          <xs:element minOccurs="0" maxOccurs="unbounded" name="simpleType" type="xs:localSimpleType"/>
        </xs:sequence>
        <xs:attribute name="memberTypes" use="optional">
          <xs:simpleType>
            <xs:list itemType="xs:QName"/>
          </xs:simpleType>
        </xs:attribute>
      </xs:extension>
    </xs:complexContent>
  </xs:complexType>
</xs:element>