Procedure Open(NX1,NY1,NX2,NY2,Forg,Back,Thick,Patrn,PatClr:Word;
                   KeepBackground:Boolean);

    This opens a  window  from  NX1,NY1  (top  left)  to  NX2,NY2 (bottom
    right) using  forground  colour  Forg  and  background  colour  Back.
    The window border is of thickness  Thick  and  the window interior is
    painted with pattern Patrn (see the  Pascal online help for available
    patterns) and pattern colour PatClr.

    This should be the first procedure  you call for the window.  It must
    never be called again until a Close is called.

    The window initialises its own personal buttons (to NIL).

    It is up to the  programmer  to  ensure  there  is  sufficient memory
    available for the procedure to save the background.

    If KeepBackground =  False  then  the  background is not saved and is
    assumed  to  be  a  solid  colour  (Back).    The  window  cannot  be
    hidden or moved  without  information  loss,  that is, the window can
    move, but what is in the  window  dissapears  from  the screen.  This
    is called a destructive window.

    If  however  KeepBackground  =   True,   moves  and  hides  are  non-
    destructive.

    Note that the Borland EGAVGA  driver  that  comes with Turbo Pascal 6
    does not support images >  64  kb.   I  recommend you use a different
    BGI driver.