         }
     }
 
-    /// Returns the view controller being navigated away from
+    /**
+    Return origin view controller.
+
+    - parameter transitionContext: an optional `UIViewControllerContextTransitioning`.
+
+    - returns: an optional `UIViewController`.
+    */
     func fromViewController(transitionContext: UIViewControllerContextTransitioning?) -> UIViewController? {
         return transitionContext?.viewControllerForKey(UITransitionContextFromViewControllerKey)
     }
 
-    /// Returns the view controller being navigated to
+    /**
+    Return destination view controller..
+
+    - parameter transitionContext: an optional `UIViewControllerContextTransitioning`.
+
+    - returns: an optional `UIViewController`.
+    */
     func toViewController(transitionContext: UIViewControllerContextTransitioning?) -> UIViewController? {
         return transitionContext?.viewControllerForKey(UITransitionContextToViewControllerKey)
     }
 
-    /// Returns the container view for the transition context
+    /**
+    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()
     }

                completion: completion)
    }

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

        }
    }

    /**
    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,
