<xs:attribute name="Purpose" use="optional">
    <xs:annotation>
        <xs:documentation xml:lang="en">Used to specify the purpose of the discount pricing.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="Airline">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The discount pricing is from the airline.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Custom">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The discount pricing is a custom discount.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>