This post is from the Activity iPhone Duo UIKit Q&A.
Only Home updates layout when the size class changes. Various screens are pushed and set their table and scroll heights once from the screen size. Does every controller in a navigation stack, including ones that are not visible, receive viewWillTransition(to:with:)? For forms and lists on the inner display, is readableContentGuide the width we should use, and does it update during the fold?