/**
  *		This function is a singleton method used to instantiate the EEM_Message_Template_Group object
  *
  *		@access public
  *		@return EEM_Question instance
  */
 public static function instance()
 {
     // check if instance of EEM_Message_Template_Group already exists
     if (self::$_instance === NULL) {
         // instantiate Espresso_model
         self::$_instance = new self();
     }
     // EEM_Message_Template_Group object
     return self::$_instance;
 }