What is the responder chain?
The gist
The responder chain is a linked list of UIResponder objects through which an event climbs until someone handles it. Each responder either handles the event or passes it to its next responder. The order: view → its superview → … → if the view is a controller's view, the controller itself → the superview of the controller's view (or the presenting controller) → UIWindow → UIWindowScene → UIApplication → AppDelegate (which is also a UIResponder).
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