public static function toString ($v, $enhanced = true)
  {
    if (isset($v)) {
      if ($v instanceof \Closure)
        return '<i>(native code)</i>';
      elseif (is_bool ($v))
        return $v ? '<span class=__type>true</span>' : '<span class=__type>false</span>';
      elseif (is_string ($v)) {
        $l = strlen (self::RAW_TEXT);
        return substr ($v, 0, $l) == self::RAW_TEXT ? substr ($v, $l)
          : sprintf ("<i>'</i>%s<i>'</i>", htmlspecialchars ($v));
      }
      elseif ($v instanceof \PowerString)
        return sprintf ("<i>(</i>%s<i>)'</i>%s<i>'</i>",
          $enhanced ? self::shortenType (\PowerString::class) : typeOf ($v),
          htmlspecialchars ($v));
      elseif (!is_array ($v) && !is_object ($v))
        return htmlspecialchars (str_replace ('    ', '  ', trim (print_r ($v, true))));
    }
    return $enhanced ? sprintf ('<span class=__type>%s</span>', self::getType ($v)) : typeOf ($v);
  }