xlink:show

<xs:attribute name="show" default="embed">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="new"/>
      <xs:enumeration value="replace"/>
      <xs:enumeration value="embed"/>
      <xs:enumeration value="other"/>
      <xs:enumeration value="none"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>