Expose and document the junk and popular sets as attributes of the SequenceMatcher object.

self.junk = junk
self.popular = popular

Deprecate the then unneeded and undocumented isbjunk and isbpopular functions, currently defined as
    self.isbjunk = junk.__contains__
    self.isbpopular = popular.__contains__
(and slightly modify the matcher function that localizes and uses one of the above).

Question, (how) do we  document deprecation/removal of undocumented function?

In discussions that included Tim Peters, the idea of exposing the tuning parameters of the heuristic was discussed. Now that the heuristic can be turned off, I think this is YAGNI until someone specifically requests it.