bug#81512: [PATCH] Add command `outline-occur'

>> It's fine for packages to add own rules to the existing value of
>> 'display-buffer-default-alist'.  Then the last package wins
>> when the first rule will match, e.g.:
>>
>>    (((category . bookmark-jump)
>>       display-buffer-for-package-2
>>       (package . 2))
>>     ((category . bookmark-jump)
>>       display-buffer-for-package-1
>>       (package . 1))
>
> This means that once the user has loaded package-2, the behavior
> prescribed by the previously loaded package-1 is lost.  This cannot
> happen if package designers are told to let-bind that variable.

We can't tell authors what they should do.  But it's fine to add
a suggestion in the docstring that it's intended to be used with let-bind.