code: Rule XcomMargins() {
  		return Sequence(
  			FirstOfS(String("botmargin"),
  					String("topmargin"),
  					String("leftmargin"),
  					String("rightmargin")),
  				//suppressSubnodes()
  			OptionalS(String("=")),
  			WSPS(), XcomNumber(), XcomUnit()
  		).label(XcomMargins);
  	}
docs: xcom-margins ::= ("botmargin" / "topmargin" / "leftmargin" / "rightmargin")
  1*WSP xcom-number xcom-unit