title: Should I use an NSViewController for this?
body: <p>I want my application to have a single document but several screens without resorting to several windows. What's the best way to achieve this? I'm thinking of using a single NSPersistentDocument that will start with a NSViewController displaying a set of controls and then swap that view for another NSViewController.</p>
  
  <p>My question is: is this the correct use of NSViewControllers? Can it even be done? And if the answer to both is yes, how do I swap a view for another in a document?</p>