<oPopUp>:select(<nPosition>) --> self

        <nPosition> is a numeric value that indicates the position in the
        pop-up menu of the item to be selected.

        select() is a method of the PopUpMenu class that is used for changing
        the selected item.  Its state is typically changed when one of the
        arrow keys is pressed or the mouse's left button is pressed when its
        cursor is within the pop-up menu's screen region.