code: Rule Lydian() {
  		return Sequence(IgnoreCase("lyd"),
  			Optional(Sequence(IgnoreCase("i"),
  				Optional(Sequence(IgnoreCase("a"),
  					Optional(IgnoreCase("n"))
  				))
  			))
  		).label(Lydian).suppressSubnodes();
  	}
docs: major with sharp 4th
  
  lydian ::= "lyd" ["i" ["a" ["n"]]]