Clef positions

[Peter Chubb]

I find the documentation of clefs in the reference manual obscure.

It says (version 1.3.137, abbreviating slightly):

\clef clefname;

is shorthand for:

 \property Staff.clefGlyph = @var{glyph associated with clefname} 
  \property Staff.clefPosition = @var{clef Y-position for clefname}
  \property Staff.clefOctavation = @var{extra pitch of clefname}

where
...
\clef  bass; is F clef on the fourth line.
...

But the clefPosition seems strange to me -- If I set it to 2 to get,
say, an F clef on the second line, the clef comes out on the fourth
line.  I suspect from experiment that Y-position here doesn't mean
staffline, but offset from the middle of the staff.

And surely a clef needs four parameters, anyway:
    -- the glyph
    -- which note it represents (currently only C F or G)
    -- which staffline
    -- which octave
??

PeterC