Some of IDL's object classes are subclassed from more generic IDL objects. You may see references to the generic IDL objects when using IDL's HELP procedure to get information on an object, or when you use the OBJ_ISA or OBJ_CLASS functions. You may also notice that the generic objects are not documented in this section. This is not an oversight.
We have chosen not to document the workings of the more generic objects from which the IDL graphics objects are subclassed because we reserve the right to make changes to their operation. We strongly recommend that you do not use the undocumented object classes directly, or subclass your own object classes from them. Research Systems, Inc. does not guarantee that user-written code that uses undocumented features will continue to function in future releases of IDL.