Re: Several serious problems

[Richard Stallman]

    If the specified coding system is totally inappropriate for
    the buffer, highlighting them will results in huge amount of
    overlays and also it takes long time to finish the job.

That is true.

      If
    we limit the number of highlighting, it may give users
    incorrect information (i.e. non-highlighted characters seems
    to be encodable).

It could highlight the first N runs of such characters, and display a
message saying "Many more unencodable characters found--type WHATEVER
to view them".  WHATEVER could be the same command with a prefix
argument.

What do you think of that?