What is a formal definition of a first responder in iOS?

Question

I understand that a first responder object is the receives a callback signal according to input activity, etc and that it will bubble it up the chain until a responder willing t

Answer 1

Before the window object keep in mind one before process please.

When the application object gets touch objects or others converts to its event object and it dispatches it to the window object. And window object sends to the most appropriate object to handle the event ( responder chain ). So window instance has property first responder instance no more one.

weak var firstResponder: NSResponder? { get }