Changing TAC definition to pass 4 or 6 hex digits

  <xs:simpleType name="TAC">

    <xs:restriction base="xs:string">

      <xs:pattern value="[A-Fa-f0-9]{4}"></xs:pattern>

      <xs:pattern value="(?:[A-Fa-f0-9]{2}){2,3}"></xs:pattern>

    </xs:restriction>

  </xs:simpleType>