bug#846: Bug in handling invisible text, and bug in Pmail.

[Richard M. Stallman]

    > I think this is a bug in the command loop's handling of invisible
    > text -- it should not be the case that C-f C-b changes point.

    There are various desirable behaviors w.r.t invisible text, and you
    can't have them all at the same time.

I know that better than anyone, and I thought about this a long time.
The command loop used to have code to make sure that there weren't
two different possible point values that would display as the same place.

    It's been with us for a while now

Did you change my decision?  If so, when did that happen?

                                      and hasn't caused any real bug report
    yet (other than reports such as this one, that is; which complain on
    principle rather than because of some real problem

It was a real problem, even though Pmail should not use invisible text
for this.  It led to confusing behavior in this case, and it will be
confusing in every case where invisible text is used.

If people have not complained, maybe it is because the use of 
invisible text is rare.  What other modes use invisible text?