We should be able to look at see if the child has a data-react-id attribute but isn't rendered by this copy of React and consequently warn.

See https://groups.google.com/forum/#!topic/reactjs/mdwfKKJ0L2Q.

* @param {?function} callback function triggered on completion
   * @return {ReactComponent} Component instance rendered in `container`.
   */
  render: function(nextElement, container, callback) {
    return ReactMount._renderSubtreeIntoContainer(null, nextElement, container, callback);
  },
  /**
   * Unmounts and destroys the React component rendered in the `container`.
   * See https://facebook.github.io/react/docs/top-level-api.html#reactdom.unmountcomponentatnode
   *
   * @param {DOMElement} container DOM element containing a React component.
   * @return {boolean} True if a component was found in and unmounted from
   *                   `container`
   */
  unmountComponentAtNode: function(container) {
    
    
    
    
    warning(
      ReactCurrentOwner.current == null,
      'unmountComponentAtNode(): Render methods should be a pure function ' +
      'of props and state; triggering nested component updates from render ' +
      'is not allowed. If necessary, trigger nested updates in ' +
      'componentDidUpdate. Check the render method of %s.',
      ReactCurrentOwner.current && ReactCurrentOwner.current.getName() ||
        'ReactCompositeComponent'
    );
    invariant(
      container && (