private static int parseWhitespaceBackwards(@NotNull String s, int index) {
    if (index < 0) return -1;
    if (Character.isWhitespace(s.charAt(index))) return index;
    index = parseUnicodeEscapeBackwards(s, index, Character::isWhitespace);
    if (index < 0) return -1;
    index--;
    int nBackSlashes = 1;
    if (index >= 0 && s.charAt(index) == '\\') {
      nBackSlashes++;
      nBackSlashes += countBackSlashes(s, index - 1);
    }
    return nBackSlashes % 2 == 0 ? -1 : index + 1;
  }
private static int parseWhitespaceBackwards(@NotNull String s, int index)