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 minLen = Math.min(string1.length, string2.length);
  for (var i = 0; i < minLen; i++) {
    if (string1.charAt(i) !== string2.charAt(i)) {
      return i;
    }
  }
  return string1.length === string2.length ? -1 : minLen;
}
/**
 * @param {DOMElement|DOMDocument} container DOM element that may contain
 * a React component
 * @return {?*} DOM element that may have the reactRoot ID, or null.
 */
function getReactRootElementInContainer(container) {
  if (!container) {
    return null;
  }
  if (container.nodeType === DOC_NODE_TYPE) {
    return container.documentElement;
  } else {
    return container.firstChild;
  }
}
function internalGetID(node) {