isOpen

        Contains a logical value that indicates whether the list is visible.
        A value of true (.T.) indicates that the list is visible; otherwise a
        value of false (.F.) indicates that it is not visible.  When
        ListBox:dropDown is false (.F.), ListBox:isOpen is always true (.T.);
        otherwise, ListBox:isOpen is true (.T.) during the period of time
        between calling ListBox:open() and ListBox:close().