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.

invariant(
      container.nodeType !== DOC_NODE_TYPE,
      'You\'re trying to render a component to the document but ' +
        'you didn\'t use server rendering. We can\'t do this ' +
        'without using server rendering due to cross-browser quirks. ' +
        'See ReactDOMServer.renderToString() for server rendering.'
    );
    if (transaction.useCreateElement) {
      while (container.lastChild) {
        container.removeChild(container.lastChild);
      }
      DOMLazyTree.insertTreeBefore(container, markup, null);
    } else {
      setInnerHTML(container, markup);
      ReactDOMComponentTree.precacheNode(instance, container.firstChild);
    }
    if (__DEV__) {
      var hostNode = ReactDOMComponentTree.getInstanceFromNode(container.firstChild);
      if (hostNode._debugID !== 0) {
        ReactInstrumentation.debugTool.onHostOperation(
          hostNode._debugID,
          'mount',
          markup.toString()
        );
      }
    }
  },
};
module.exports = ReactMount;