public function get_default(): ?string
  {
    if (
      ($id_opt = $this->from_path('default')) &&
      ($all = $this->pref->get_all($id_opt))
    ){
      $id = false;
      foreach ( $all as $a ){
        if ( !empty($a['id_user']) ){
          $id = $a['id_alias'];
          break;
        }
        else if ( !empty($a['id_group']) ){
          $id = $a['id_alias'];
          break;
        }
        else if ( !empty($a['public']) ){
          $id = $a['id_alias'];
          break;
        }
      }
      return $id;
    }
	return null;
  }