NAME
        DisplayBeep -- Flash the video display.

    SYNOPSIS
        DisplayBeep( screen )
                     A0

        VOID DisplayBeep( struct screen * );

    FUNCTION
        "Beeps" the video display by flashing the background color of the
        specified screen.  If the screen argument is NULL, every screen
        in the display will be beeped.  Flashing everyone's screen is not
        a polite thing to do, so this should be reserved for dire
        circumstances.

        The reason such a routine is supported is because the Amiga has
        no internal bell or speaker.  When the user needs to know of
        an event that is not serious enough to require the use of a requester,
        the DisplayBeep() function may be called.

        New for V36:  Intuition now calls DisplayBeep through the
        external library vector.  This means that if you call setfunction()
        to replace DisplayBeep with an audible beep, for example, then
        your change will affect even Intuition's calls to DisplayBeep.

    INPUTS
        screen = pointer to a screen.  if null, every screen in the display
           will be flashed

    RESULT
        None

    NOTES
        Since this function changes color zero of the affected screen(s),
        surprising results could occur if the screen's owner reading
        colors or perhaps cycling them.

    BUGS

    SEE ALSO