// back: Function?// A function to be called when this state is reached via the user// clicking the back button.// forward: Function?// Upon return to this state from the "back, forward" combination// of navigation steps, this function will be called. Somewhat// analgous to the semantic of an "onRedo" event handler.// changeUrl: Boolean?|String?// Boolean indicating whether or not to create a unique hash for// this state. If a string is passed instead, it is used as the// hash.