interpolation

<xsd:attribute name="interpolation" use="optional" default="linear">
  <xsd:simpleType>
    <xsd:restriction base="xsd:string">
      <xsd:enumeration value="floor"/>
      <xsd:enumeration value="middle"/>
      <xsd:enumeration value="ceiling"/>
      <xsd:enumeration value="linear"/>
      <xsd:enumeration value="cubic"/>
    </xsd:restriction>
  </xsd:simpleType>
</xsd:attribute>