QQPercentDrivenInteractiveTransition is a drop-in replacement for UIPercentDrivenInteractiveTransition for use in custom container view controllers.
Why do you need it? Because Apples own UIPercentDrivenInteractiveTransition calls undocumented methods on your custom UIViewControllerContextTransitioning objects.
Note that this class can be used with UIKits standard container view controllers such as UINavigationController, UITabBarController and also for presenting modal view controllers.