<xsd:complexType name="heightType"> <xsd:simpleContent> <xsd:extension base="xsd:nonNegativeInteger"> <xsd:attribute name="datum" type="datumType" use="required" /> <xsd:attribute name="height-units" type="height-unitsType" use="optional" /> </xsd:extension> </xsd:simpleContent> </xsd:complexType>