title: In an AppDelegate, how is the main UIWindow instantiated?
body: <p>A snippet of the default code in a Master-Detail Xcode project</p>
  
  <hr>
  
  <p>AppDelegate.m</p>
  
  <pre><code>- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions
  {
      // Override point for customization after application launch.
   UINavigationController *navigationController = (UINavigationController *)self.window.rootViewController;  // *** here ***
      MasterViewController *controller = (MasterViewController *)navigationController.topViewController;
      controller.managedObjectContext = self.managedObjectContext;
      return YES;
  }
  </code></pre>
  
  <p>AppDelegate.h </p>
  
  <pre><code>@property (strong, nonatomic) UIWindow *window;
  </code></pre>
  
  <p>I am aware that @synthesize just sets the accessor methods, and no initialization happens automagically. But how does <code>window</code> have a non-nil <code>rootViewController</code> if it is never explicitly initialized? Is this just Xcode init'ing behind the scenes?</p>