<xsd:attribute name="type" use="required">
    <xsd:simpleType>
        <xsd:restriction base="xsd:string">
            <xsd:enumeration value="sustained" />
            <xsd:enumeration value="rtma-sustained" />
            <xsd:enumeration value="gust" />
            <xsd:enumeration value="transport" />
            <xsd:enumeration value="cumulative34" />
            <xsd:enumeration value="cumulative50" />
            <xsd:enumeration value="cumulative64" />
            <xsd:enumeration value="incremental34" />
            <xsd:enumeration value="incremental50" />
            <xsd:enumeration value="incremental64" />
        </xsd:restriction>
    </xsd:simpleType>
</xsd:attribute>