Gnome provides utility functions for relaying simple messages to
      the user and asking simple questions. The utility functions
      serve two purposes: first, they keep programmers from writing
      dozens of identical dialogs; second, they let the user choose
      whether messages should appear in dialogs or on the appbar. The
      main set of utility functions assume that your app uses the
      GnomeApp widget, and that one is visible at the
      time they're called. These functions have a dialog backend and
      an appbar backend. The dialog backend is exposed, so you can use
      it directly if you have no GnomeApp widget available.  The
      GnomeApp functions do not
      assume you have an appbar available; you should use them even if
      your app has no appbar. In some cases it makes a difference (for
      example, dialog can be positioned relative to the
      GnomeApp).