private static @NotNull TreeElement drillDown(@NotNull TreeElement start) {
    TreeElement cur = start;
    while (cur.getCachedLength() < 0) {
      TreeElement child = cur.getFirstChildNode();
      if (child == null) {
        break;
      }
      cur = child;
    }
    return cur;
  }
private static @NotNull TreeElement drillDown(@NotNull TreeElement start)