function is_utf8(&$string)
	{
		if ($string === mb_convert_encoding(mb_convert_encoding($string, "UTF-32", "UTF-8"), "UTF-8", "UTF-32")) {
			return true;
		}

		if ($this->ignore_invalid_utf8) {
			$string = mb_convert_encoding(mb_convert_encoding($string, "UTF-32", "UTF-8"), "UTF-8", "UTF-32");
			return true;
		}

		return false;
	}