rankBasis

<xs:attribute name="rankBasis" default="confidence">
  <xs:simpleType>
    <xs:restriction base="xs:string">
      <xs:enumeration value="confidence"/>
      <xs:enumeration value="support"/>
      <xs:enumeration value="lift"/>
      <xs:enumeration value="leverage"/>
      <xs:enumeration value="affinity"/>
    </xs:restriction>
  </xs:simpleType>
</xs:attribute>