Re: New package `outline-occur'

>> If you find it useful, and given that it only depends on built-in
>> functionalities (Outline and Occur), would it make sense to add it to
>> core?  Otherwise, what about GNU ELPA?
>
> I think this is a strong candidate for the core, since the actual code
> (excluding documentation) is about 10 lines of code.  I've CC'ed Juri
> for a second opinion, but I think you can already draft up a patch
> against emacs.git.

Indeed, it's completely suitable for core since it's just
one command 'outline-occur'.  But we need to make minor changes
before installing it in outline.el.

Since 'outline-mode' and 'outline-minor-mode' use dedicated
keymaps, we need to bind a new key (the suggested key 'M-o'
is the most intuitive) under the existing prefix keys
'outline-mode-prefix-map' and 'outline-minor-mode-prefix'.

Also instead of 'outline-occur-regexp-override-alist',
the proper way is to add a new buffer-local variable
(e.g. 'outline-occur-regexp' nil by default)
that can be set in the mode hooks.

Also overriding 'occur-hook' with 'pop-to-buffer' is not
the right way to customize the buffer display behavior.
Either the command can override with 'display-buffer-overriding-action',
or we can leave the customization to users with 'display-buffer-alist'.