function traverseAllChildren(children, callback, traverseContext) {
  if (children == null) {
    return 0;
  }

  return traverseAllChildrenImpl(children, '', callback, traverseContext);
}
@ReactInputSelection: React input selection module. Based on Selection.js,
but modified to be suitable for react and has a couple of bug fixes (doesn't
assume buttons have range selections allowed).
Input selection module for React.