If the lookingForNothing method cannot find a field that needs filling, it sends the message "cardFilled".
If you are building a card with no buttons, that takes some action as soon as it is filled, this is a good method to override. It is usually best to have the overriding method push an "OK" button on the screen. That way, you can use the button yourself on local logins, but not bother the user with it.
The default cardFilled method sends a displayButtons message. The method invoked by this message displays all pushable buttons for the user to select from -- note that the first letter of these buttons must be unique.