The user may define subclasses of this class.
Horizontal, vertical and time accuracy values are defined using the CoordinateAccuracy domain. The higher order source is considered as more accurate and serves as a basis of comparison. It may be specified as 'control' to indicate the control information given under the SpatialReferencing subclass, as 'tile' for the tile data given under ContentLocation, or as some other string. (Note that more than one instance of coordinate accuracy may be given. This may be used for example to state that 95% of the points are within certain bounds, that 90% are within other bounds, etc.)