bug#20466: 25.0.50; REGRESSION in `isearch-mode-map': <backspace> is not translated to DEL

[Drew Adams <drew.adams@oracle.com>]

> The "why" part was answered by Artur, who pointed to the bug report
> which triggered that change.

That reports a problem.  It doesn't imply that the chosen fix is
the best fix.

> > It is an incompatible change, and I see nothing in NEWS about it.
> 
> It's not really incompatible, but I agree that it would be good to
> document the change, although I don't believe we document changes in
> keybindings in general.

> if you want to change the binding of DEL, you had better changed
> the binding of Backspace accordingly at the same time, because
> there's no guarantee Backspace will not be bound in any particular
> mode.  So why you are showing a use case that violates this simple
> rule?

That's certainly a useful rule for users to keep in mind, and it
applies to all key translations.  But it has not been necessary
in the past to take it into account for Isearch.  That's all.

Dunno whether such a rule/reminder is mentioned in the Emacs docs,
or even where it should be mentioned (key translations are not
something that most users read about).  Even if it were mentioned
in the doc about key translations, I doubt that would help most
users who might stumble on this.  Think of the many users who
have asked about shifted keys (a similar translation gotcha).

FWIW: I don't mind this change, personally (I don't bind `DEL' in
`isearch-mode-map').  I'm just pointing out that it might not be
expected, and that some users will likely scratch their heads
trying to figure out what's going on.

What the best thing to do about it is now (maybe nothing?), I
don't know.