The defobj library currently includes the CreateDrop and Object_s superclasses used by other libraries. For user objects in Swarm simulations the SwarmObject superclass in the objectbase library packages all required behavior of these superclasses into a single, simpler superclass.
The defobj library also provides support for custom-generated classes, such as those which implement separate phases of the standard create protocol. (See generated phase classes in the Advanced Usage Guide.) Subclassing from custom-generated classes is still not officially supported, because the framework for custom class generation is still being finalized. Custom-generated classes are currently used only in the defobj, collections, and activity libraries; these libraries document the specific classes that provide subclassing support.
In general, classes that implement a library are not automatically available for use as superclasses. Any library must document those specific superclasses that are valid for user classes to subclass from, along all the rules that a user subclass must follow when implementing new behavior.