gml:NilReasonType defines a content model that allows recording of an explanation for a void value or other exception.<br/>gml:NilReasonType is a union of the following enumerated values:<br/>- inapplicable there is no value<br/>- missing the correct value is not readily available to the sender of this data. Furthermore, a correct value may not exist<br/>- template the value will be available later<br/>- unknown the correct value is not known to, and not computable by, the sender of this data. However, a correct value probably exists<br/>- withheld the value is not divulged<br/>- other:text other brief explanation, where text is a string of two or more characters with no included spaces<br/>and<br/>- anyURI which should refer to a resource which describes the reason for the exception<br/>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.<br/>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.<br/>