Re: master 8a88f3ed5ae: Add `outline-occur' command and `display-buffer-default-alist' variable

>> Everything there must be rigid and deterministic in the choice of how
>> windows display buffers.
>
> Yes, but getting your Emacs to this point is not easy.  Emacs'
> unpredictable buffer display behavior is one of the top complaints of
> new and intermediate users.  Unpredictable window placement is very
> annoying and does not let them build a working mental model of Emacs.

Adding a command like describe-repeat-maps, e.g. describe-display-buffer
could help to better describe the effect of display-buffer-alist.
Also an option for debugging to display the matched rule in the echo area
after displaying every buffer.

> When they decide to read the "Displaying Buffers" section of the manual,
> they are completely overwhelmed by the number of options and precedences
> between them, and the structure of display-buffer-alist and the action
> arguments.

Maybe we need more interactive commands that help to build
display-buffer-alist.  Such as e.g. add-file-local-variable-prop-line
helps to build the file local variables, and customize-dirlocals
with add-dir-local-variable helps to build the dir-local file.

> The reason for adding both display-buffer-overriding-alist and
> display-buffer-default-alist make sense to me.  But then I internalized
> how display-buffer-alist (& co) work a long time ago and I can
> understand this extra complexity as incremental changes.  I was
> remarking that the overall level of complexity of display-buffer keeps
> growing, which is not a good thing.

OTOH, new variables are not intended for user customization,
so most users don't need to know about them.