From Xojo Documentation
Identifies iOS UI layouts that can be used as a screen.
A screen can contain a single iOSView, an iOSSplitView (consisting of a main view and a detail view) or an iOSTabBar, which consists of multiple views.
Because iOSScreenContent is an interface, you will not work with it directly. You will instead work with the classes that implement it: iOSSplitView, iOSTabBar and iOSView.