public static function add(string $messageType, string $message): void
    {
        $_SESSION[self::SESSION_KEY][$messageType][] = $message;
    }
public static function add(string $messageType, string $message): void
    {
        $_SESSION[self::SESSION_KEY][$messageType][] = $message;
    }
public static function add ( string $ messageType , string $ message ) : void { $ _SESSION [ self :: SESSION_KEY ] [ $ messageType ] [ ] = $ message ; }
Add a flash message. Message type can be anything, but preferably use one of the constants defined in this class.

@param string $messageType
@param string $message
Add a flash message . Message type can be anything but preferably use one of the constants defined in this class .