Eli Zaretskii <eliz@gnu.org> writes:

> I'm not sure we should reveal those details here.  Hidden buffers are
> handled specially in many places in Emacs, and I don't think we spell
> that out in every doc string.
>
> Stefan, WDYT?

On first approximation, I'd tend to agree with you, but I think Martin
made a good point later in this discussion, when he said the following.

martin rudalics <rudalics@gmx.at> writes:

> I think a new automatically buffer-local variable, say
> 'display-via-make-frame', would not harm anyone.

So I think we could install Martin's proposed patch, with NEWS and doc
changes of course.