reason

<xs:attribute name="reason" use="required">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="not authorized"/>
      <xs:enumeration value="insufficient priority"/>
      <xs:enumeration value="other"/>
      <xs:enumeration value="not available"/>
      <xs:enumeration value="syntax"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>