code: public static function printCharCode($code)
      {
          if ($code === null) {
              return '<EOF>';
          }
  
          return $code < 0x007F
              // Trust JSON for ASCII.
              ? json_encode(self::chr($code))
              // Otherwise print the escaped form.
              : '"\\u' . dechex($code) . '"';
      }
docs: @param int|null $code
  
  @return string