The objects of the CallbackOption class are used only as a child of the objects of the CallbackOptions class. Each object serves for setting up site reaction when you press certain page active elements listed in the PostBackControls property. Updatable controls are listed in the ControlsList property. Also, the programmer has an opportunity to change the behaviour of browser navigation buttons (it is determined by the DisableBackButton property of the page) by setting up the BackButtonMode property.