Class, isSelected, item);
      }
      if (this.selectedAttribute) {
        this.toggleAttribute(this.selectedAttribute, isSelected, item);
      }
      this._selectionChange();
      this.fire('iron-' + (isSelected ? 'select' : 'deselect'), {item: item});
    },

    _selectionChange: function() {
      this._setSelectedItem(this._selection.get());
    },

    // observe items change under the given node.
    _observeItems: function(node) {
      return Polymer.dom(node).observeNodes(function(mutations)