<simpleType name="NullEnumeration">
    <annotation>
        <appinfo source="urn:opengis:specification:gml:schema-xsd:basicTypes:3.1.1">basicTypes.xsd</appinfo>
        <documentation> Some common reasons for a null value:   
			
        innapplicable - the object does not have a value
        missing - The correct value is not readily available to the sender of this data.  
                           Furthermore, a correct value may not exist.
        template - the value will be available later
        unknown - The correct value is not known to, and not computable by, the sender of this data. 
                           However, a correct value probably exists.
        withheld - the value is not divulged 
        
        other:reason - as indicated by "reason" string
        
        Specific communities may agree to assign more strict semantics when these terms are used in a particular context.  
      </documentation>
    </annotation>
    <union>
        <simpleType>
            <restriction base="string">
                <enumeration value="inapplicable" />
                <enumeration value="missing" />
                <enumeration value="template" />
                <enumeration value="unknown" />
                <enumeration value="withheld" />
            </restriction>
        </simpleType>
        <simpleType>
            <restriction base="string">
                <pattern value="other:\w{2,}" />
            </restriction>
        </simpleType>
    </union>
</simpleType>