MusicXML Clefs

Re: https://github.com/w3c/musicxml/issues/316#issuecomment-631558362
"You might be better off asking questions like this on our mailing list
<https://lists.w3.org/Archives/Public/public-music-notation/> instead of
GitHub. We try to reserve GitHub issues for ideas and bug reports as
opposed to user support questions."

I posted this because it sounded like a "bug" to me, that the musicXML
format allows note and line in <clef> definition, and allows offsetting the
octave, but does not say what octave to use.

If MuscXML only supports clefs by name - G, F, C, etc. - why does it
include the "line" attribute. Are their "G" clefs which have the G on a
different line. Is there is a clef like G/5 instead of G/2?

-- 
Al