<xs:simpleType name="empty-string">
    <xs:annotation>
        <xs:documentation>
				A primitive type used to permit null values, represented
				by the empty string, for data types other than the
				xs:string type. Combined with the base data type in a
				union, the custom data type can permit validation of the
				XML instance document where the underlying type is
				integer for example. In that case, the values permitted
				are any integer OR the empty string.
			</xs:documentation>
    </xs:annotation>
    <xs:restriction base="xs:string">
        <xs:length value="0" />
    </xs:restriction>
</xs:simpleType>