gml:NilReasonType

gml:NilReasonType defines a content model that allows recording of an explanation for a void value or other exception.
gml:NilReasonType is a union of the following enumerated values:
-	inapplicable there is no 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:text other brief explanation, where text is a string of two or more characters with no included spaces
and
-	anyURI which should refer to a resource which describes the reason for the exception
A particular community may choose to assign more detailed semantics to the standard values provided. Alternatively, the URI method enables a specific or more complete explanation for the absence of a value to be provided elsewhere and indicated by-reference in an instance document.
gml:NilReasonType is used as a member of a union in a number of simple content types where it is necessary to permit a value from the NilReasonType union as an alternative to the primary type.