code: Rule XcomStaves() {
  		return Sequence("staves",
  				OneOrMore(WSP()).suppressNode(),
  				StaveVoice(),
  				ZeroOrMore(Sequence(BarStaves(), StaveVoice())))
  			.label(XcomStaves);
  	}
docs: xcom-staves ::= "staves" 1*WSP stave-voice *( bar-staves stave-voice)