This Implementation Specification provides interfaces for general positioning, coordinate systems, and coordinate transformations. Coordinates can have any number of dimensions. So this specification can handle 2D and 3D coordinates, as well as 4D, 5D etc.
In order to handle any number of dimensions, this specification provides a Coordinate System package that could eventually replace the Spatial Reference package contained in the Simple Features specifications. However, it has been designed to work in conjunction with Simple Features during any transition period.