TRUE
CLIPS> (load "visible.clp")
##~~~
[MSGFUN6] visible.clp, Line 16: Private slot 'bar' of class 'A' cannot be accessed directly by handlers attached to class 'B'

ERROR:
(defmessage-handler MAIN::B fribban
   ()
   ?self:bar
   )
@!
FALSE
CLIPS> (go)
[MSGPASS3] Static reference to slot 'foo' of class 'A' does not apply to instance [b] of class 'B'.
[PRCCODE4] Execution halted during the actions of message-handler 'woz' primary in class 'A'
[PRCCODE4] Execution halted during the actions of deffunction 'go'.
FALSE
CLIPS> (dribble-off)