         }
     }
 
-    /// Push Transition
+    /**
+    Push fromViewController onto navigation stack.
+
+    - parameter toOffset:           vertical offset at which to start interactive animation.
+    - parameter toViewController:   destination view controller.
+    - parameter fromViewController: origin view controller.
+    - parameter containerView:      container view for transition context.
+    - parameter completion:         completion handler.
+    */
     func push(toOffset: CGFloat = 0.0,
         toViewController: UIViewController,
         fromViewController: UIViewController,

                completion: completion)
    }

    /// Pop Transition
    func pop(toViewController: UIViewController,
        fromViewController: UIViewController,
        containerView: UIView,

        }
    }

    /**
    Return origin view controller.

    - parameter transitionContext: an optional `UIViewControllerContextTransitioning`.

    - returns: an optional `UIViewController`.
    */
    func fromViewController(transitionContext: UIViewControllerContextTransitioning?) -> UIViewController? {
        return transitionContext?.viewControllerForKey(UITransitionContextFromViewControllerKey)
    }

    /**
    Return destination view controller..

    - parameter transitionContext: an optional `UIViewControllerContextTransitioning`.

    - returns: an optional `UIViewController`.
    */
    func toViewController(transitionContext: UIViewControllerContextTransitioning?) -> UIViewController? {
        return transitionContext?.viewControllerForKey(UITransitionContextToViewControllerKey)
    }

    /**
    Return the container view for the given transition context.

    - parameter transitionContext: an optional `UIViewControllerContextTransitioning`.

    - returns: the container `UIView` for the transition context.
    */
    func containerView(transitionContext: UIViewControllerContextTransitioning?) -> UIView? {
        return transitionContext?.containerView()
    }
