What is a default font?

[martin rudalics <rudalics@gmx.at>]

I just noticed that my implementation of 'window-default-font-height'
is likely wrong.  The fault is all mine but I think that, in a sense,
'default-font-height', 'default-font-width', 'default-line-height' and
'face-font' are to blame as well.

In particular, the 'face-font' doc-string should tell that it returns
a value for the current buffer if FRAME is nil or omitted and a value
for FRAME if it is non-nil, disregarding the current buffer in that
case entirely.  If that's the correct interpretation of that function.
So far I can't make heads or tails of it.

The other functions are IMO ill-specified for the case where the
current buffer does not appear on the selected frame.  Using values
returned by 'frame-parameter', 'frame-char-height' and
'frame-char-width' in that case can be misleading and present simple
guesses at the best.

Personally, I would prefer two types of functions.  One for getting
the default face font of a buffer alone (including remapping) and one
for the default face font of a frame.  But I don't know enough about
fonts, their remapping and their relationship to frames to tell what
really makes sense here.

martin