All of the 3ds Max object types (i.e. instances of classes derived from Object) accessible in MAXScript are represented by instances of the MAXWrapper and derived classes. These are declared in the header file maxscrpt/maxobj.h. The wrapped reference is a reference created with ReferenceMaker::ReplaceReference(). The MAXWrapper class inherits from both Value and ReferenceMaker. This reference allows MAXScript to be notified of MAX-side changes to the object, particularly deletion.
The classes that derive from Value:
The class MAXBitMap is used to wrap 3ds Max bitmaps, but it is not a ReferenceMaker because bitmaps in MAX can not be a reference target.
The MAXSubAnim which is used to wrap objects which derive from Animatable and are accessible inside other Max objects via the Animatable::SubAnim() function. This is used in MAXScript to wrap the modifier gizmo sub-objects, for example.