private static int findSlashU(@NotNull String s, int index) {
    if (s.charAt(index) != 'u') return -1;
    // 'u' can appear multiple times
    do {
      index--;
    } while (index >= 0 && s.charAt(index) == 'u');
    if (index < 0 || s.charAt(index) != '\\') return -1;
    return index;
  }
private static int findSlashU(@NotNull String s, int index)