Explain ContainerWidget

Author: bbrk24

Sources/UIKitBackend/Widget.swift

@@ -276,6 +276,13 @@ class WrapperWidget<View: UIView>: BaseViewWidget {
     }
 }
 
+/// The root class for widgets who are passed their children on initialization.
+///
+/// If a widget is passed an arbitrary child widget on initialization (as opposed to e.g. ``WrapperWidget``,
+/// which has a specific non-widget subview), it must be a view controller. If the widget is
+/// a view but the child is a controller, that child will not be connected to the parent view
+/// controller (as a view can't know what its controller will be during initialization). This
+/// widget handles setting up the responder chain during initialization.
 class ContainerWidget: BaseControllerWidget {
     let child: any WidgetProtocol