private static int countBackSlashes(@NotNull String s, int index) {
    int nBackSlashes = 0;
    while (index >= 0) {
      int start = s.charAt(index) == '\\' ? index : parseUnicodeEscapeBackwards(s, index, c -> c == '\\');
      if (start == -1) break;
      nBackSlashes++;
      index = start - 1;
    }
    return nBackSlashes;
  }
private static int countBackSlashes(@NotNull String s, int index)