code: function updateReferences(el) {
  		$.each(mtypes, function (i, pos) {
  			var id = marker_prefix + pos + '_' + el.id;
  			var marker_name = 'marker-'+pos;
  			var marker = getLinked(el, marker_name);
  			if (!marker || !marker.attributes.se_type) {return;} // not created by this extension
  			var url = el.getAttribute(marker_name);
  			if (url) {
  				var len = el.id.length;
  				var linkid = url.substr(-len-1, len);
  				if (el.id != linkid) {
  					var val = $('#'+pos + '_marker').attr('value');
  					addMarker(id, val);
  					svgCanvas.changeSelectedAttribute(marker_name, "url(#" + id + ")");
  					if (el.tagName === 'line' && pos == 'mid') {el = convertline(el);}
  					S.call("changed", selElems);
  				}
  			}
  		});
  	}
docs: called when the main system creates or modifies an object primary purpose is create new markers for cloned objects