anchor.diff:                                   {"state", State}]}),
       State;
   on_unknown_event(UnknownMessage, State) ->
  -    log:log(error, "unknown message: ~.0p~n in Module: ~p and handler ~p"
  -            " in pid ~p ~.0p~n in State ~.0p",
  +    log:log(error,
  +            "~n** Unknown message:~n ~.0p~n"
  +            "** Module:~n ~.0p~n"
  +            "** Handler:~n ~.0p~n"
  +            "** Pid:~n ~p ~.0p~n"
  +            "** State:~n ~.0p~n",
               [UnknownMessage,
                gc_mod(State),
                gc_hand(State),
  -             self(), pid_groups:group_and_name_of(self()), State]),
  +             self(), pid_groups:group_and_name_of(self()),
  +             State]),
       State.
   
   on_exception(Msg, Level, Reason, Stacktrace, State) ->
  
positive.code:     T1State = on_bp(Msg, State),
      Module  = gc_mod(T1State),
      Handler = gc_hand(T1State),
      T2State =
          try Handler(Msg, gc_ustate(T1State))
          catch Level:Reason ->
                  Stacktrace = erlang:get_stacktrace(),
                  case Stacktrace of
                      %% erlang < R15 : {Module, Handler, [Msg, State]}
                      %% erlang >= R15: {Module, Handler, [Msg, State], _}
                      [T | _] when
                            erlang:element(1, T) =:= Module andalso
                            erlang:element(2, T) =:= Handler andalso
                            erlang:element(3, T) =:= [Msg, T1State] andalso
                            Reason =:= function_clause andalso
                            Level =:= error ->
                          {'$gc_unknown_event',
  
negative.code:             end;
          {'$gc_unknown_event', NewState} -> NewState;
          {'$gc_exception', NewState} ->     NewState;
          unknown_event ->
              %% drop T2State, as it contains the error message
              TmpState = on_unknown_event(Msg, T1State),
              bp_step_done(Msg, TmpState);
          NewUState ->
              bp_step_done(Msg, gc_set_ustate(T1State, NewUState))
      end.
  