Interface ScreenScrollShape<Items, Failure, Returns>

The brand of a handle member that moves through its screen (a feed's nextPage, a swipeable feed's swipeToNext): the definition does not know the handle it is bound to, so the binding types the result from the handle the member is called on. returns says what comes back, or undefined when there is nothing to bring (the end of a feed): host — another instance of the screen itself; item — one of its items (Items), reached from it. The call may fail with failure; like every member it runs with the services captured when the screen entered.