gml:TimeIndeterminateValueType

These values are interpreted as follows: 
-	"unknown" indicates that no specific value for temporal position is provided.
-	"now" indicates that the specified value shall be replaced with the current temporal position whenever the value is accessed.
-	"before" indicates that the actual temporal position is unknown, but it is known to be before the specified value.
-	"after" indicates that the actual temporal position is unknown, but it is known to be after the specified value.
A value for indeterminatePosition may 
-	be used either alone, or 
-	qualify a specific value for temporal position.