code: Rule ClefName() {
  		return Sequence(
  			FirstOfS(IgnoreCase("treble"), IgnoreCase("alto"), IgnoreCase("tenor"),
  				IgnoreCase("baritone"), IgnoreCase("bass"), IgnoreCase("mezzo"),
  				IgnoreCase("soprano"), IgnoreCase("perc"), IgnoreCase("none")),
  			OptionalS(Octave())	
  			).label(ClefName).suppressSubnodes();
  	}
docs: Maybe also Doh1-4, Fa1-4
  
  clef-name ::= "treble" / "alto" / "tenor" / "baritone" / "bass"
  / "mezzo" / "soprano" / "perc" / "none"