public void startSubFlow(final InstanceID insertationPoint) {
    final RenderBox box;
    if (insertationPoint == null) {
      throw new IllegalStateException();
    }

    final RenderBox rootBox = getLayoutRoot();
    box = (RenderBox) rootBox.findNodeById(insertationPoint);
    if (box == null) {
      dontPushBoxToContext();
    } else {
      pushBoxToContext(box, false);
    }
  }