answers with a set of the message selectors in the method dictionary.
aBehavior allSelectors
does the same but includes the selectors of the superclasses.
aBehavior allInstances
answers the set of all instances of the receiver From the class comment:
My instances describe the behavior of other objects. I provide the minimum state necessary for compiling methods, and creating and running instances. Most objects are created as instances of the more fully supported subclass, Class, but I am a good starting point for providing instance-specific behavior (as in Metaclass).
Behavior is also used by code which creates objects which are not normal instances of a Class, such as Prototypes.