is an abstract service for a component which offers a more complex user
interface to users within a status bar.
A generic status bar function is represented as a text field which
provides status information to the user. A status bar controller can be
added to a status bar and provides information or functions with a more
sophisticated user interface.
A typical example for a status bar controller is the zoom level chooser
within the statusbar. It provides an option to change the zoom level of
an application.
