public function slug(string $basename): string
    {
        if (($slug = mb_strstr($basename, '/', true))) {
            return $slug; // Got what we need here.
        } elseif (($slug = mb_strstr($basename, '.php', true))) {
            return $slug; // Got what we need here.
        }
        return ''; // Failed on `[slug]/plugin.php` & `[slug].php`.
    }