Referencia para las distancias.

<xs:attribute name="reference" use="required">
    <xs:annotation>
        <xs:documentation>Referencia para las distancias.</xs:documentation>
    </xs:annotation>
    <xs:simpleType>
        <xs:restriction base="xs:string">
            <xs:enumeration value="LEFT_SHOULDER" />
            <xs:enumeration value="LEFT_ROADWAY" />
            <xs:enumeration value="LEFT_INT_ROADWAY" />
            <xs:enumeration value="LEFT_INT_SHOULDER" />
            <xs:enumeration value="CENTERLINE" />
            <xs:enumeration value="RIGHT_INT_SHOULDER" />
            <xs:enumeration value="RIGHT_INT_ROADWAY" />
            <xs:enumeration value="RIGHT_ROADWAY" />
            <xs:enumeration value="RIGHT_SHOULDER" />
        </xs:restriction>
    </xs:simpleType>
</xs:attribute>