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.

var rootEl = getReactRootElementInContainer(container);
  if (rootEl) {
    var inst = ReactDOMComponentTree.getInstanceFromNode(rootEl);
    return !!(inst && inst._hostParent);
  }
}
function getHostRootInstanceInContainer(container) {
  var rootEl = getReactRootElementInContainer(container);
  var prevHostInstance =
    rootEl && ReactDOMComponentTree.getInstanceFromNode(rootEl);
  return (
    prevHostInstance && !prevHostInstance._hostParent ?
    prevHostInstance : null
  );
}
function getTopLevelWrapperInContainer(container) {