function add_nofollow_acf($field)
{
  $field = preg_replace_callback('/<a[^>]*href=["|\']([^"|\']*)["|\'][^>]*>([^<]*)<\/a>/i',
    function ($m) {
      if (strpos($m[1], "md7.info") === false) {
        return '<a href="'.$m[1].'" rel="nofollow noopener noreferrer" target="_blank">'.$m[2].'</a>';
      } else {
        return '<a href="'.$m[1].'" target="_blank">'.$m[2].'</a>';
      }
    },
    $field
  );
  return $field;
}