code: function getLinked(elem, attr) {
  		var str = elem.getAttribute(attr);
  		if(!str) {return null;}
  		var m = str.match(/\(\#(.*)\)/);
  		if(!m || m.length !== 2) {
  			return null;
  		}
  		return S.getElem(m[1]);
  	}
docs: elem = a graphic element will have an attribute like marker-start attr - marker-start, marker-mid, or marker-end returns the marker element that is linked to the graphic element