closure

<xs:attribute name="closure" use="required">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="openClosed"/>
      <xs:enumeration value="openOpen"/>
      <xs:enumeration value="closedOpen"/>
      <xs:enumeration value="closedClosed"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>