/**
  * @desc Returns number comments
  * @param string $module_id the module identifier
  * @param integer $id_in_module id in module used in comments system
  * @param string $topic_identifier topic identifier (use if you have several comments system)
  * @return string number comments
  */
 public static function get_number_comments($module_id, $id_in_module, $topic_identifier = CommentsTopic::DEFAULT_TOPIC_IDENTIFIER)
 {
     return CommentsManager::get_number_comments($module_id, $id_in_module, $topic_identifier);
 }