docs: private static char[] asUnicodeHexEscape(char c) {
      // Equivalent to String.format("\\u%04x", (int)c);
      char[] r = new char[6];
      r[0] = '\\';
      r[1] = 'u';
      r[5] = HEX_DIGITS[c & 0xF];
      c >>>= 4;
      r[4] = HEX_DIGITS[c & 0xF];
      c >>>= 4;
      r[3] = HEX_DIGITS[c & 0xF];
      c >>>= 4;
      r[2] = HEX_DIGITS[c & 0xF];
      return r;
    }