Glossary
The vocabulary Apple uses for iPhone Duo, defined in one place.
- App Resizability
- The new name, in Xcode 27.1, for the app modernization skill Apple introduced in the WWDC26 talk Modernize your UIKit app. It now supports SwiftUI and iPhone Duo, and Apple presents it as a way to check that an app follows adaptive layout best practices.
See also: Device Hub
- Arrangement
- A layout container that places a primary and a secondary view across iPhone Duo's poses, using size classes, the view's aspect ratio and active division regions as input. Available as ArrangementView in SwiftUI and UIArrangementViewController in UIKit, with split and overlay styles. Keep navigation containers outside it.
See also: Split arrangement, Overlay arrangement, Division region, Size class
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Designing for iPhone Duo (Human Interface Guidelines)
- Axis behavior
- Overrides which axis a bar item uses on iPhone Duo. Items with a symbol move into the vertical bar; text-only items and custom views stay horizontal. .verticalPreferred lets a custom view join the vertical bar; .horizontalOnly keeps an item, such as one that switches between symbol and text, horizontal. Set with .axisBehavior() in SwiftUI or item.axisBehavior in UIKit.
See also: Vertical bar
- Device Hub
- The Xcode 27.1 simulator interface for iPhone Duo, with on-screen control buttons to open, close, rotate and fold the device so a layout can be checked in every pose.
See also: Pose, App Resizability
- Division region
- A reserved region that divides the iPhone Duo inner display into separate usable areas. The hinge is the example: it is active only while the device is folded and has zero width when the device is flat.
See also: Reserved region, Occlusion region, Pose
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463)
- Hinge angle
- The physical angle of the iPhone Duo hinge, reported through onHingeChange in SwiftUI and UIHingeInteraction in UIKit, with states closed, partially open and fully open. Apple's guidance is to use it for interactions and effects only, never for layout decisions.
See also: Pose, Division region
Source: Leverage multiple displays and scenes on iPhone Duo (Tech Talk 111464)
- Multiple scenes
- Support for more than one instance of an app at once, declared with UIApplicationSupportsMultipleScenes. iPhone Duo is the first iPhone to support this. New windows can only be created on the inner display; the outer display is reserved.
See also: Scene accessory, Split View multitasking
Source: Leverage multiple displays and scenes on iPhone Duo (Tech Talk 111464)
- Occlusion region
- A reserved region that covers part of the display rather than dividing it. On iPhone Duo the inner front-facing camera is one; it is present only while the camera is active, when the system moves UI aside. Background content may pass beneath an occlusion region; interactive content should not.
See also: Reserved region, Division region, Safe area
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Designing for iPhone Duo (Human Interface Guidelines)
- Overlay arrangement
- An arrangement style that places the secondary view on top of the primary one. When iPhone Duo is partially folded, the two move to either side of the fold instead. The natural replacement for a ZStack with a clear foreground and background.
See also: Arrangement, Split arrangement, Pose
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Designing for iPhone Duo (Human Interface Guidelines)
- Pose
- A physical configuration of iPhone Duo — closed, partially folded like a book, propped on a table, or fully open flat — each combined with an orientation. Xcode's Device Hub simulates poses with on-screen controls to open, close, rotate and fold.
See also: Division region, Device Hub, Hinge angle
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Prepare your app for iPhone Duo (Tech Talk 111461)
- Reserved region
- An area of the screen that system hardware or UI claims, reported by ReservedRegion in SwiftUI and UIViewReservedRegion in UIKit from iOS 27.1. Regions come in two kinds — division and occlusion — and each has an active and an inactive state.
See also: Division region, Occlusion region, Arrangement
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Prepare your app for iPhone Duo (Tech Talk 111461)
- Safe area
- The region of a view not covered by system UI. On iPhone Duo safe areas and layout margins are asymmetric, so each side must be handled independently — code that doubles one inset to account for the opposite side is wrong on this device.
See also: Occlusion region, Reserved region
- Scene accessory
- Supplementary UI shown on one iPhone Duo display while the app's main UI runs on the other — a teleprompter or subject preview on the outer display, for example. The camera capture accessory is available only when the app is full screen on the inner display with an active camera session.
See also: Multiple scenes, Pose
Source: Leverage multiple displays and scenes on iPhone Duo (Tech Talk 111464)
- Size class
- A coarse description of available layout space, either compact or regular in each dimension. On iPhone Duo the inner display is regular in both dimensions and leaves room for sidebars, while the outer display is compact-width and regular-height.
See also: Pose, Split View multitasking
- Split arrangement
- An arrangement style that divides the available area between a primary and a secondary view: side by side when the space is wider than tall, stacked when taller than wide. The natural replacement for an HStack or VStack of two related views.
See also: Arrangement, Overlay arrangement, Division region
Source: Strike a pose with adaptive layouts on iPhone Duo (Tech Talk 111463), Designing for iPhone Duo (Human Interface Guidelines)
- Split View multitasking
- Side-by-side app layout on the iPhone Duo inner display. All apps participate whether or not they opt in, so any app can be given an arbitrary fraction of the display at a moment the user chooses.
See also: Size class, Multiple scenes
Source: Leverage multiple displays and scenes on iPhone Duo (Tech Talk 111464), Prepare your app for iPhone Duo (Tech Talk 111461)
- Vertical bar
- The shared side region where navigation, toolbar and tab bar controls lay out vertically on iPhone Duo, preserving vertical space for content. It applies on the outer display and on the inner display in landscape; the inner display in portrait keeps horizontal bars. Standard containers get it under the iOS 27.1 SDK.
See also: Axis behavior, Size class
Source: Raise the bar with iPhone Duo (Tech Talk 111462), Designing for iPhone Duo (Human Interface Guidelines)