bug#51210: Customizable other-window-for-scrolling

[Juri Linkov <juri@linkov.net>]

>> >> There are also nice commands: M-<home> (beginning-of-buffer-other-window)
>> >> and M-<end> (end-of-buffer-other-window), but for no reason they recenter
>> >> the other window after moving to the beginning/end.
>> >> 
>> >> It would be better to remove this disservice:
>> >
>> > This is age-old behavior.  Why change it because you happen to dislike
>> > it?
>> 
>> The problem is that with its current implementation, it's unusable:
>> when the window height is 75 lines, then typing M-<end> leaves
>> half-screen empty.
>
> If you start typing at the end of the buffer, the half-empty window
> will immediately make sense.

You can't start typing because it's in another window.

> Are you using scroll-conservatively, perhaps?  If so, I can understand
> why you don't like this behavior.  But that's your subjective opinion,
> and I see no reason to change this by default.

This problem is reproducible in emacs -Q:
visit e.g. TODO with 'C-h C-t', split windows with 'C-x 3',
and type 'M-<end>'.  Then another window is recentered.

>> But fortunately this can be fixed since Emacs 28 introduced a new key
>> C-M-S-l to recenter the other window, so it's now easy to type it
>> when the user needs to recenter the other window.
>
> Great.

So everyone who wants to recenter, can type: 'M-<end> M-C-S-l'.