Undo boundary

[Juri Linkov <juri@jurta.org>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:
>> It would be nice if the undo history would recognize that:
>>   "any char" 
>>     followed by 
>>   m-x delete-backward-char
>
>> Is functionally the same as.
>
>>   "any char"
>>     followed by
>>   m-x undo
>
>> I admit it's easier said than done.
>
> What would be the benefit?
> I.e. in which cases would it make a diference?

It seems OP refers to the fact that `command_loop_1' has the built-in
constant value 20 for undo-boundary of self-inserting characters.

It makes sense to make it configurable.  Often `undo' undoes too much
characters than needed.  To get them back, the user has to break the
undo chain, redo undoing of the last 20 characters, and to start
to delete the needed amount of characters with delete-backward-char.

This is too inconvenient and also breaks the undo history unnecessarily.
Users with high keyboard repeat rate would prefer to change this value
to 1, press C-_ key, and hold it while `undo' undoes characters one
at a time.

However, this is useful only for the last inserted characters.
It would be a nuisance to undo characters one at a time for earlier
character insertions.  For them even the value 20 is too small.
It is desirable to undo whole blocks of earlier character insertions,
not in chunks of 20 characters.

-- 
Juri Linkov
http://www.jurta.org/emacs/