How to use storyboard UICollectionReusableView(s) with custom layouts?

If I don't use a subclass of flow layout anytime I add a UICollectionReusableView to a collection view it ends up in the scene dock and not registered by the collection view. How can this be done?


I know I can do everything in code, or create a nib backed view. What is it that flow layout is doing to allow storyboard UICollectionReusableView(s) to work properly?