Can anyone show a simple code snippet about the usage of this property? I tried to create a UIWindow inside the main window, and set the canResizeToFitContent to true. However, when I added to it some sub view, the sub view didn't fit into the UIWindow. Actually, this sub view was located in another place far away from the UIWindow I created. Additionally, The documentation says, the content should be constraint-based. What does 'constraint-based' mean?