[The light dawns, as the pieces connect together] The pseudoclass 'MyButton' would then consist of all widgets with 'MyButton' inserted into its bindtags list.  Similarly for 'Editor'. I presume that a) tk has the equivalent of a master bind dict mapping bindtags to dicts mapping event sequences strings to event handlers, and b) .bind_class(cname, evseq, func) does the equivalent of "tagdict.get(cname, {})[evseq] = func".

I also notice that the introspective versions of .bind... call will let us discover the pre-defined bindings on difference systems and check our alterations.  Anyway, thanks.  I will experiment when ready to refactor bindings.  In the meanwhile, I will apply the patch and close this.