Root object of a class definition hierarchy.
 The ClassHier object is a toplevel object in a class volume, and act as
 the anscestor to the class definition hierarchy.
 It should be named 'Class', and there kan only be one $ClassDef object in a
 ClassVolume.

 Below the $ClassHier object, all the classes in the volume are defined with
 $ClassDef objects.

See also

• $ClassDef