bug#37840: Missing in the Emacs manuals:

[martin rudalics]

> Thanks for your reply. Working on the stuff, I encountered the following 
problem: If, in “ display-buffer-alist”, I have the entry:
>
>        ("[ ]?Packages[ ]?" (display-buffer-reuse-window 
display-buffer-pop-up-frame)
>         (pop-up-frame-parameters
>          (tool-bar-lines . 1)
>    (left . 1)
>    (left-fringe . 2)
>          (top . 0)
>    (height . 65)
>    (width . 149)
>    (font . "SF MONO-18")
>          (line-spacing . 3)
>    ))
>
> then, contrary to what is promised, this does not pop up a new
> frame.

There's no promise that 'display-buffer-alist' controls the behavior
of 'switch-to-buffer'.  The latter should be used interactively (via
C-x b) only.  But since that's practically impossible given the sheer
mass of occurrences of 'switch-to-buffer' in the Emacs code base, Juri
added the 'switch-to-buffer-obey-display-actions' option.  If that is
non-nil, your use case should work.

> I figured out that the problem goes away if, in
> “packages.el”, I replace in the defun “list-packages” the code
> (switch-to-buffer buf) by (pop-to-buffer buf). My question is how to
> do this on the level of customizing “display-buffer-alist”. I didn’t
> find anything in this regard in the manuals.

'switch-to-buffer' preferably shows its buffer in the same (selected)
window.  'pop-to-buffer' has no such preference.

martin