<oListBox>:prevItem() --> self

        prevItem() is a method of the ListBox class that is used for changing
        the selected item from the current item to the one immediately before
        it.  If necessary, prevItem() will call its display() method to
        ensure that the newly selected item is visible.

        This message is meaningful only when the ListBox object has input
        focus.

        Note:  When present, the scroll bar is automatically updated to
        reflect the new first visible item in the list when the call to
        ListBox:prevItem() causes the list to be scrolled.