Re: master 2ef6f943abd: Add option to control default outlining in 'C-h b'

[Eli Zaretskii <eliz@gnu.org>]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Juri Linkov <juri@linkov.net>,  michael_heerdegen@web.de,
>   emacs-devel@gnu.org,  orontee@gmail.com
> Date: Wed, 26 Apr 2023 10:17:08 +0200
> 
> >>>>> On Tue, 25 Apr 2023 21:00:08 +0300, Eli Zaretskii <eliz@gnu.org> said:
> 
>     >> >> So I see no reason to remove 'custom-function'.
>     >> >> What could be done instead is to add a new choice
>     >> >> 'custom-predicate'.
>     >> >
>     >> > The suggestion is not to remove custom-function.  The suggestion is to
>     >> > require that the function returns a boolean, to mean whether to hide
>     >> > or not to hide a heading, instead of requesting that the function
>     >> > itself hides/unhides the headings.
>     >> >
>     >> > What is the purpose of requesting a custom function to actually
>     >> > hide/unhide the headings, i.e. to know enough about the structure and
>     >> > internal details of Outline mode to do its job?
>     >> 
>     >> How the user would be able to use 'outline-show-branches'
>     >> in the custom function, and not to use 'outline-hide-entry'?
> 
>     Eli> Sorry, I don't understand the question and its relevance.  Maybe
>     Eli> Robert does.
> 
> In the current implementation, the user is free to write a function
> that uses any of the outline-show/hide functions to get the effect
> they desire. If we replace that with just a predicate function, then
> theyʼre effectively restricted to `outline-hide-entry' and
> `outline-show-subtree'.
> 
> I guess we could add `predicate', to be checked before
> `custom-function', if set. If we do that, we definitely need to
> document which outline functions are available. 100% backwards
> compatible as well 😄

Or maybe we stay with custom-function, but allow it to return symbols
other than nil and t, so it could, for example, return
'outline-show-branches'?