     /**
     Cancels any actions registered to run for a specified object.
     
+        canvas.cancel(self)
+
     :param: observer An object whose actions are to be removed from the notification center.
     */
     public func cancel(observer: AnyObject) {

    /**
    An action to run on receipt of a given event.
    
    :param: event The notification name to listen for
    :param: run A block of code to run when the receiver "hears" the specified event name
    */

    /**
    Posts a new notification originating from the receiver.
    
        canvas.addTapGestureRecognizer { location, state in
            self.canvas.post("tapped")
        }

    :param: event The notification name for the event
    */
    internal func post(event: String) {
