docs: private static void printCodePointAsTwoHexDigits(Appendable out, int c)
          throws IOException
      {
          String s = Integer.toHexString(c);
          out.append("\\x");
          if (s.length() < 2) {
              out.append(ZERO_PADDING[2-s.length()]);
          }
          out.append(s);
      }