How to position a UI element at the very top right corner of a window or page?

To place a UI element in the top right corner of a window or page in iOS, Auto Layout with NSLayoutConstraint or the visual editor in Interface Builder are usually used.

Example with NSLayoutConstraint in code:

let view = UIView()
view.translatesAutoresizingMaskIntoConstraints = false
parentView.addSubview(view)

NSLayoutConstraint.activate([
    view.topAnchor.constraint(equalTo: parentView.safeAreaLayoutGuide.topAnchor),
    view.trailingAnchor.constraint(equalTo: parentView.trailingAnchor)
])

Here, view will be anchored to the top edge of the safe area and the right edge of the parent view. The Safe Area accounts for notches and the status bar so that the element does not end up underneath them.