Notify class is superclass of all other MUI classes. Its main purpose is to handle MUI's notification mechanism, but it also contains some other methods and attributes useful for every object.
Because Notify class is the super class for all other MUI classes, you can use all of its attributes with all other MUI classes. For example, you can use Notify.HelpNode to add online help reference to MUI gadgets or you could use Notify.AppMessage to add MUI objects to the app message handler.