/**
  * Listing the active users for ajax.
  * Entering 'forum#XX' (or any last part of 'forum' with #XX) looks for 
  * member of the XX ID without username.
  * Entering integer looks for member with XX in username or empty username 
  * and that ID.
  * @param string $q Username query
  * @return string|\yii\web\Response
  */
 public function actionFieldlist($q = null)
 {
     if (!Yii::$app->request->isAjax) {
         return $this->redirect(['default/index']);
     }
     return User::getMembersList($q);
 }