function slugify()
    {
        $text = (string) $this;

        // replace non letter or digits by -
        $text = preg_replace('~[^\pL\d]+~u', '-', $text);

        // transliterate
        $text = iconv('utf-8', 'us-ascii//TRANSLIT', $text);

        // remove unwanted characters
        $text = preg_replace('~[^-\w]+~', '', $text);

        // trim
        $text = trim($text, '-');

        // remove duplicate -
        $text = preg_replace('~-+~', '-', $text);

        // lowercase
        $text = strtolower($text);

        if (empty($text))
            return 'n-a';

        return new self($text);
    }