The responder chain is based on the layers of UI Elements in the UIWindow when a tap gesture is detected. If the first object doesn't have an IBAction to detect the tap event, the responsibility of handling the gesture is passed to the element below it, and so on, until an IBAction detects the tap. This allows you to present UI elements above a button but if they "appear" transparent, a user can still tap the button behind them because those elements will not have a touch gesture recognizer attached to them.