<xs:attribute name="Usage" use="optional">
    <xs:annotation>
        <xs:documentation xml:lang="en">Used to specify how the discount is to be applied.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="Plus">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The discount being applied is an increase to the fare.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Minus">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The discount being applied is subtracted from the fare.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>