<oPopUp>:setItem(<nPosition>, <oMenuItem>) --> self

        <nPosition> is a numeric value that indicates the position in the
        pop-up menu of the item that is being retrieved.

        <oMenuItem> is the MenuItem object that replaces the one in the pop-
        up menu specified by <nPosition>.

        setItem() is a method of the PopUpMenu class that is used for
        replacing a MenuItem object after it has been added to a pop-up menu.
        After the setItem() method is called, the display()method needs to be
        called in order to refresh the menu.  It is not allowed to call the
        display() method for the currently opened pop-up menu in the code
        block of the menu items.  Otherwise, there are screen refresh
        problems especially if the code block has also increased the number
        of items in the pop-up menu.