code: function(event) {
          var propagate = true;
          if(!this.clustering) {
              this.clearCache();
              this.features = event.features;
              this.cluster();
              propagate = false;
          }
          return propagate;
      }
docs: Method: cacheFeatures
  Cache features before they are added to the layer.
  
  Parameters:
  event - {Object} The event that this was listening for.  This will come
  with a batch of features to be clustered.
  
  Returns:
  {Boolean} False to stop features from being added to the layer.