xChannelSelector

<xs:attribute name="xChannelSelector" default="A">
  <xs:simpleType>
    <xs:restriction base="xs:token">
      <xs:enumeration value="R"/>
      <xs:enumeration value="G"/>
      <xs:enumeration value="B"/>
      <xs:enumeration value="A"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>