code: Rule TitleFields() {
  		return Sequence(
  			ZeroOrMoreS(FirstOfS(Comment(), Xcommand(), Tex())),
  			OneOrMoreS(
  				SequenceS(
  					FieldTitle(),
  					ZeroOrMoreS(FirstOfS(Comment(), Xcommand(), Tex()))
  				)
  			)
  		).label(TitleFields);
  	}
docs: title-fields ::= *(comment / xcommand / tex) 1*(field-title *(comment / xcommand / tex))