UIScene

New in iOS 13, is scenes.

Can have each scene be entirely independent. Can have each scene be dedicated to a specific task.

This uses UIWindowScene and UISceneSession.

UIWindowScene goes between the UIScreen and UIWindow level.

Scenes contains UI, created by system on demand, destroyed by system when unused.

Going to adopt UIWindowSceneDelegate.

Basically, moving a lot of UIApplicationDelegate methods into UIWindowSceneDelgeate methods.