Apple's example for Camera overlay - APLViewController.m

Question

I really find the example from apple a good start for working around the UIImagePickerController:

APLViewController.m

However, there is something that seems core to the overlay that I don't understand. The project works perfectly fine I just hope someone can explain me what happens here:

     /* 
     Load the overlay view from the OverlayView nib file. 
     Self is the File's Owner for the nib file, so the overlayView outlet is set 
     to the main view in the nib. Pass that view to the image picker controller 
     to use as its overlay view, and set self's reference to the view to nil. 
     */ 
    [[NSBundle mainBundle] loadNibNamed:@"OverlayView" owner:self options:nil]; 
    self.overlayView.frame = imagePickerController.cameraOverlayView.frame; 
    imagePickerController.cameraOverlayView = self.overlayView; 
    self.overlayView = nil; 

I have done other sample projects with overlay and all is fine. It's just that the way it's done here must be for a good reason. Thank you for clarifying, I'm hoping this will help me code my overlay the right way.