>> But then we can't discriminate minibuffer-less from normal frames by
 >> looking at the parameter value only.
 >
 > We can look at what window-frame returns for that window, can't we?

Tediously so, yes.

 >> This goes both ways.  With (2) Emacs would choose nil when
 >> ‘set-frame-position’ explicitly asks for a window.  And with no
 >> 'minibuffer' specified we'd have to return t or a window in any case.
 >
 > Yes, but IMO nil is not a meaningful value.  If we know better, we
 > should return a more concrete value.

Sounds convincing.

 > Yes, of course, the current situation is not impossible.  We are
 > talking about improving it.

I attached a preliminary version of the code changes.  Please have a
look.

Thanks, martin