code: function() {
          var layer;
          // walk through all map layers, because we want to keep the order
          for(var i=0; i<this.map.layers.length; ++i) {
              layer = this.map.layers[i];
              if(OpenLayers.Util.indexOf(this.layers, layer) != -1) {
                  layer.renderer.moveRoot(this.renderer);
              }
          }
      }
docs: Method: collectRoots
  Collects the root nodes of all layers this control is configured with
  and moveswien the nodes to this control's layer