Adds a Component type variable. On client side the variable value will be
     * a terminal specific reference to corresponding component on client side
     * implementation. When updated from client side, terminal will map the
     * client side component reference back to a corresponding server side
     * reference.
Adds a Component type variable. On client side the variable value will be
     * a terminal specific reference to corresponding component on client side
     * implementation. When updated from client side, terminal will map the
     * client side component reference back to a corresponding server side
     * reference. | PaintTarget.java