title: How to set parentViewController in UIViewController?
body: <p>The parentViewController property of UIViewController is readonly, but I am nesting custom view controllers and would like to use this property. </p>
  
  <p>However, since it is readonly, and I found no other way to set this property, my quesion is: how <em>do</em> I set it?</p>
  
  <p>Obviously, UINavigationController can set the property somehow in -pushViewController, and so can -presentModalViewController, so it must be possible.</p>
  
  <p>I am aware that I can just add my own UIViewController property, but I'm sure that parentViewController is, in principle, the correct property.</p>