code: function (layers) {
  		var id, layer;
  
  		for (id in layers) {
  			layer = layers[id];
  
  			// Make sure we do not override markers that do not belong to THIS group.
  			if (this.hasLayer(layer)) {
  				// Need to re-create the icon first, then re-draw the marker.
  				layer.setIcon(this._overrideMarkerIcon(layer));
  			}
  		}
  	}
docs: Re-draws the icon of the supplied markers.
  To be used in singleMarkerMode only.
  @param layers Array(L.Marker)|Map(L.Marker) list of markers.
  @private