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.

}
          rootElementSibling = rootElementSibling.nextSibling;
        }
      }
    }
    var shouldReuseMarkup =
      containerHasReactMarkup &&
      !prevComponent &&
      !containerHasNonRootReactChild;
    var component = ReactMount._renderNewRootComponent(
      nextWrappedElement,
      container,
      shouldReuseMarkup,
      nextContext
    )._renderedComponent.getPublicInstance();
    if (callback) {
      callback.call(component);
    }
    return component;
  },
  /**
   * Renders a React component into the DOM in the supplied `container`.
   * See https://facebook.github.io/react/docs/top-level-api.html#reactdom.render
   *
   * If the React component was previously rendered into `container`, this will
   * perform an update on it and only mutate the DOM as necessary to reflect the
   * latest React component.
   *
   * @param {ReactElement} nextElement Component element to render.
   * @param {DOMElement} container DOM element to render into.