code: Rule NthRepeat() {
  		return FirstOf(
  			SequenceS(String("[").label(Barline).suppressSubnodes(),
  				FirstOfS(NthRepeatNum(), NthRepeatText())),
  			SequenceS(
  				Sequence(ZeroOrMore(':'), "|").label(Barline).suppressSubnodes(),
  				NthRepeatNum())
  			).label(NthRepeat);
  	}
docs: nth-repeat ::= "[" ( nth-repeat-num / nth-repeat-text )
  
  for compatibility, accepts (":|" / "|") nth-repeat-num