backKey message backKey Sent to the current card of the defaultStack when the hardware back button is pressed.
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on backKey

answer "You pressed the back key" with "Okay"

end backKey

Added. User Interaction searchKey Message menuKey Message Handle the backKey message to perform an action when the back button is pressed. The backKey message is sent to the current card of the default stack when the hardware back button is pressed.

If this message is passed or not handled, then the engine automatically quits.