function wp_nav_menu_aslwordpress( $nav_menu, $args ) {
    $nav_menu = preg_replace("~\s+id=\".+?\"~", "", $nav_menu);

    $nav_menu = preg_replace_callback(
        "~\s+class=\"(.+?)\".*?>[^<]*<([^\s]+)~s",
        function ($class) {
            if (in_array("current-menu-item", preg_split("~\s+~", $class[1])))
            {
                return '><' . $class[2] . ' class="active"';
            }
            else
            {
                return '><' . $class[2];
            }
        },
        $nav_menu
    );

    $nav_menu = preg_replace("~\s+aria-.+?\".+?\"~", "", $nav_menu);

    $nav_menu = preg_replace("~<button.+?/button>~", "", $nav_menu);

    do {
        $tmp = $nav_menu;

        $nav_menu = preg_replace('#<([^ >]+)[^>]*>([[:space:]]|&nbsp;)*</\1>#', '', $nav_menu);
    } while ( $nav_menu !== $tmp );

    $xml = simplexml_load_string($nav_menu);

    for ($i = 0; $i < count($xml->li); $i++)
    {
        if ($xml->li[$i]->ul)
        {
            $content = $xml->li[$i]->ul->asXML();

            preg_match("~<a.+?>(.+?)</~s", $xml->li[$i]->asXML(), $title);

            $xml->li[$i] = "<a class=\"open_m\" href=\"#\">" . $title[1] . "</a> <div class=\"drop_down_block drop-block\">" .
            $content . "</div>";

            $xml->li[$i]->addAttribute('class', 'item item-drop');
        }
    }

    $nav_menu = html_entity_decode($xml->asXML(), ENT_NOQUOTES, 'UTF-8');

    $nav_menu = preg_replace("~<[?]xml[^>]+>\s*~", "", $nav_menu);

    return $nav_menu;
}

add_filter( 'wp_nav_menu', 'wp_nav_menu_aslwordpress', 10, 2 );