code: Rule XcomMidi() {
  		return Sequence(String("midi"),
  				OptionalS(String("=")),
  				OneOrMore(WSP()),
  				FirstOf(MidiChannel(), MidiProgram(), MidiTranspose()))
  			.label(XcomMidi);
  	}
docs: xcom-midi ::= "midi" 1*WSP (midi-channel / midi-program / midi-transpose)