code: public static function add($strMessage, $strType, $strScope=TL_MODE)
  	{
  		if ($strMessage == '')
  		{
  			return;
  		}
  
  		if (!\in_array($strType, static::getTypes()))
  		{
  			throw new \Exception("Invalid message type $strType");
  		}
  
  		System::getContainer()->get('session')->getFlashBag()->add(static::getFlashBagKey($strType, $strScope), $strMessage);
  	}
docs: Add a message
  
  @param string $strMessage The message text
  @param string $strType    The message type
  @param string $strScope   An optional message scope
  
  @throws \Exception If $strType is not a valid message type