https://developer.apple.com/documentation/uikit/uiview/1622574-transition specifies for the animation parameter: This parameter must not be NULL. Yet the animation parameter is defined as (() -> Void)? and passing nil seems to work fine, performing an animation on the latest update to the with view.

UIContentSizeCategory implements the usual comparison operators through an NS_REFINED_FOR_SWIFT macro, but does not declare Comparable conformance. Implementing it is as easy as extension UIContentSizeCategory: Comparable {} Is there a reason why Comparable is not implemented by default?