title: Difference between viewControllers and childViewControlle for UINavigationController
body: <pre><code>fileprivate func test() {
  
          guard let w = self.view.window else {
              print("no window")
              return
          }
          guard let rootvc = w.rootViewController as? UINavigationController else {
              print("no rootvc")
              return
          }
  
          for vc in rootvc.childViewControllers {
              print("CHILD \(vc)")
          }
  
          for vc in rootvc.viewControllers {
              print("VC \(vc)")
          }
  }
  </code></pre>
  
  <p>the code above shows the same. But whats the difference between <code>childViewControllers</code> and <code>viewControllers</code> ?</p>