docs: function(partialProps, callback) {
      // This is a deoptimized path. We optimize for always having an element.
      // This creates an extra internal element.
      var element = this._pendingElement || this._currentElement;
      this._pendingElement = ReactElement.cloneAndReplaceProps(
        element,
        assign({}, element.props, partialProps)
      );
      ReactUpdates.enqueueUpdate(this, callback);
    }