<xs:simpleType name="VATCodeType">
  <xs:restriction base="xs:NMTOKEN">
    <!-- Upper-case values -->
    <xs:pattern value="TAX"/>
    <!-- standard tax category -->
    <xs:pattern value="TAXEX"/>
    <!-- exempt from tax -->
    <xs:pattern value="NOTTAX"/>
    <!-- tax not applicable: outside scope of tax or free export item -->
    <xs:pattern value="RVAT"/>
    <!-- vat reverse charge, levied from the invoicee -->
    <xs:pattern value="ZERO"/>
    <!-- zero-rated tax -->
  </xs:restriction>
</xs:simpleType>