>> Would that suffice?  If so, would we use the same for
 >> 'display-buffer-pop-up-window' and 'display-buffer-at-bottom'?
 >
 > I don't know about display-buffer-pop-up-window, but for
 > display-buffer-at-bottom where the height depends on the
 > number of lines in the displayed buffer like e.g. *Completions*
 > this is not needed.

Note that 'display-buffer-at-bottom' is agnostic of the number of
lines in the displayed buffer.

We eventually need a generally applicable rule because the user might
want to add such an entry to 'display-buffer-alist'.  And we might
want a corresponding width entry for symmetry.  For the moment, we can
say that the entry is handled by 'display-buffer-below-selected' only.
In the attached two functions I renamed it to 'window-min-height' to
make it more consistent with 'window-height'.  Please have a look.

 > I think the semantics of 'min-height' should be a minimal height
 > of the displayed window wherever it can be displayed.

To amend the remaining buffer display action functions, a substantial
number of changes will have to be made.  'window-splittable-p', for
example, would need an additional MIN-SIZE argument.  And what about
'display-buffer-same-window' or 'display-buffer-in-previous-window'?

martin