splitView
The split view the screen is in: its columns, their widths, how they show.
Options
Every key, with the platforms it works on. A dashed platform means the key does nothing there.
17 options shown
Which columns show. 'automatic' leaves the choice to the system. What the user picks (the button, a swipe) lasts until the next mergeOptions. It applies when the split view is created and through mergeOptions, not when its screens appear. Every change reports a display mode change event. The earlier names are read too: 'hidden' is 'secondaryOnly', 'visible' 'oneBesideSecondary' ('twoBesideSecondary' with three columns), 'overlay' 'oneOverSecondary' ('twoOverSecondary' with three columns); 'auto' and any other string are 'automatic'.
The side of the primary column: 'leading' or 'trailing'. Another value counts as 'leading'. It applies when the split view is created, whenever a screen inside appears, and through mergeOptions.
The preferred width of the primary column. On iOS in points, applied only when set; without it, the system's width. On Android in dp, 360 by default: the width of the primary pane, which together with the 360 dp of the secondary one sets the width at which the panes stand side by side. It applies when the split view is created and at once through mergeOptions or new default options.
The smallest width of the primary column, applied only when set.
The largest width of the primary column, applied only when set.
The look behind the primary column: 'sidebar' gives it the sidebar background (noticeable in a Mac Catalyst app) and 'none' the plain one, also after 'sidebar' was set.
The widths of the middle column. It does nothing when the layout has no supplementary column.
The preferred width of the column. Without it, the width the system gives it.
The smallest width the column may take. Without it, the system's limit.
The largest width the column may take. Without it, the system's limit.
(iOS, iPadOS 26) The inspector column at the trailing edge: its widths and whether it shows.
How the columns share the width: 'tile' puts them side by side, 'overlay' lays the primary column over the secondary one, 'displace' pushes the secondary column aside, and 'automatic' leaves it to the system.
Whether the button that shows and hides the columns appears: 'always', 'never', or 'automatic', which hides it when presentsWithGesture is false.
Whether a swipe from the edge reveals a hidden column. On Android the swipe moves the secondary pane over the primary one and back, when they don't fit side by side; it applies when the split view is created and at once through mergeOptions or new default options.
Whether a three-column split view has a button that leaves only the secondary column.
The column shown on top when the split view collapses (iPhone, a narrow window, a narrow Android screen) and the layout has no compact content: 'primary' or 'secondary'. Without it, the system chooses on iOS (read when it collapses, from the final options with the defaults) and 'primary' is on top on Android. On Android 'secondary' opens the secondary pane without animation on the first narrow layout, and a new value applies at the next collapse.
An identifier for tests and accessibility tools. On Android the panes get <testID>.primary and <testID>.secondary. The back arrow of the first screen of a sliding pane takes the topBar.backButton.testID of that screen. Without it, the elements have no id. It changes with mergeOptions. On iOS the button that shows the columns gets no id: the system draws it in a column-style split view and gives no way to name it; find it by its accessibility label.