I installed the ChangeSet and ran the tests. They work as advertised.

I looked at the code as well and the use of allInstances bothers me
slightly. As stated in the comment this is slow. However, as currently
Behavior>>allSubclasses calls subclasses Behavior should get such a
method. Either it should be subclassResponsibility if Behavior is
supposed to be abstract.

Is it? The class comment states the following: "I am a good starting
point for providing instance-specific behavior (as in Metaclass)." Does
that mean, it is not abstract? There are no instances of Behavior in my
image. Has anyone used Behavior instances?

The other possibility would be to move the ivar subclasses from Class to
Behavior. This is how it is implemented in VAST 6.0.1, in Dolphin 5.1.3
and VWNC 7. I guess this might be a difficult change, though.

The method ClassDescription>>subclasses should be deleted.