I wrote:

> Hi Juri,
>
> Juri Linkov <juri@linkov.net> writes:
>
>> While testing more, I noticed one strange thing,
>> I don't know if it's intended to work this way.
[...]
> This appears to be a general problem with `completion-in-region-mode`,
> that it keeps TAB bound to `completion-at-point` after a partial
> completion, so I don't think we should attempt to handle it in
> `completion-preview` specifically.

Let me know if you think otherwise, that `completion-preview` should
handle this case specifically, although I'm pretty convinced that it's
the behavior of `completion-in-region-mode` that's not quite right here.

Either way, I'm attaching an new patch (v3) that includes
`backward-delete-char-untabify` in `completion-preview-commands` to
provide a nicer OOTB experience for Elisp (as you suggested), along with
a couple of minor optimizations and documentation improvements.


Best,

Eshel