         }
     }
     
+    
+    // MARK: Updating
+    
     private var isUpdatingViewControllers: Bool = false
+    /// Calls guarded setViewControllers on internal UIPageViewController
+    ///
+    /// - Parameters:
+    ///   - viewControllers: new view controllers.
+    ///   - direction: direction for transition.
+    ///   - animated: whether to animate.
+    ///   - completion: completion closure.
     internal func updateViewControllers(to viewControllers: [UIViewController],
                                        direction: UIPageViewControllerNavigationDirection,
                                        animated: Bool,

    }
    
    
    // MARK: Scrolling
    
    /// Scroll the page view controller to a new page.
    ///

        didSet {
            guard let currentIndex = self.currentIndex else { return }

            updateForNewCurrentIndex(currentIndex, from: oldValue)
        }
    }
    /// The relative page position that the page view controller is currently at.
