docs: function (filterType, filterCallback) {
                  // normalize callback only once
                  filterCallback = this.$normCallback(filterCallback);
                  var filterFn = filterCallback.fn, filterScope = filterCallback.scope;
                  // if not already done, we must first refresh the initial array before marking all elements:
                  this._refreshInitialArray();
                  var items = this.items;
                  var itemsLength = items.length;
                  for (var i = 0; i < itemsLength; i++) {
                      var elt = items[i];
                      var filteredIn = elt.filteredIn;
                      if (filterType == this.FILTER_SET || (filteredIn === (filterType == this.FILTER_REMOVE))) {
                          filteredIn = filterFn.call(filterScope, elt, filterCallback.args);
                          json.setValue(elt, "filteredIn", filteredIn);
                      }
                  }
              }