The error event on `<source>` elements doesn't work. Looking at #4370, it seems like there is an `onError` for `<video>` but I can't tell if that's supposed to work for `<source>` too.

The error event is useful so I can deduce which format the browser is using.

}
    }
  },
  /**
   * Receives a next element and updates the component.
   *
   * @internal
   * @param {ReactElement} nextElement
   * @param {ReactReconcileTransaction|ReactServerRenderingTransaction} transaction
   * @param {object} context
   */
  receiveComponent: function(nextElement, transaction, context) {
    var prevElement = this._currentElement;
    this._currentElement = nextElement;
    this.updateComponent(transaction, prevElement, nextElement, context);
  },
  /**
   * Updates a DOM component after it has already been allocated and
   * attached to the DOM. Reconciles the root DOM node, then recurses.
   *
   * @param {ReactReconcileTransaction} transaction
   * @param {ReactElement} prevElement
   * @param {ReactElement} nextElement
   * @internal
   * @overridable
   */
  updateComponent: function(transaction, prevElement, nextElement, context) {
    var lastProps = prevElement.props;
    var nextProps = this._currentElement.props;
    switch (this._tag) {