docs: function() {
          var activated = OpenLayers.Strategy.prototype.activate.apply(this, arguments);
          if (activated) {
              this.cache = [];
              this.layer.events.on({
                  "beforefeaturesadded": this.handleAdd,
                  "beforefeaturesremoved": this.handleRemove,
                  scope: this
              });
          }
          return activated;
      }