<xs:attribute name="RangePosition" use="optional">
    <xs:annotation>
        <xs:documentation xml:lang="en">Specifies whether this is the first or last traveler reference number in a range.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:NMTOKEN">
            <xs:enumeration value="First">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The first number in a range.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
            <xs:enumeration value="Last">
                <xs:annotation>
                    <xs:documentation xml:lang="en">The last number in a range.</xs:documentation>
                </xs:annotation>
            </xs:enumeration>
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>