code: function() {
          var activated = OpenLayers.Control.prototype.activate.call(this);
          if(activated) {
              for (var i=0, len=this.layers.length; i<len; i++) {
                  var layer = this.layers[i];
                  if (layer && !this.wfsCache[layer.id]) {
                      var options = {
                          url: layer.url,
                          params: {
                              SERVICE: "WMS",
                              VERSION: layer.params.VERSION,
                              LAYERS: layer.params.LAYERS,
                              REQUEST: "DescribeLayer"
                          },
                          callback: this.parseDescribeLayer,
                          scope: {layer: layer, control: this}
                      };
                      OpenLayers.Request.GET(options);
                  }
              }
          }
          return activated;
      }
docs: APIMethod: activate
  Activate the control. Activating the control will perform a SLD WMS
  DescribeLayer request followed by a WFS DescribeFeatureType request
  so that the proper symbolizers can be chosen based on the geometry
  type.