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 CallWindowProc()       Passes messages information to a specific procedure
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   Syntax:              CallWindowProc( <nWndProc>, <hWnd>, <nMsg>, <nWParam>,
                                        <nLParam> )  --> <uReturn>

   The CallWindowProc function passes message information to the specified
   window procedure.

   Parameters:

   <nWndProc>         Specifies the procedure-instance address of the previous
                      window procedure.

   <hWnd>             Identifies the window that will receive the message.

   <nMsg>             Specifies the message.

   <nWParam>          Specifies 16 bits of additional message-dependent
                      information.

   <nLParam>          Specifies 32 bits of additional message-dependent
                      information.


   Returns:           The return value specifies the result of the message
                      processing and depends on the message sent.

   Observations:      The CallWindowProc function is used for window
                      subclassing. Normally, all windows with the same class
                      share the same window procedure. A subclass is a window
                      or set of windows belonging to the same window class
                      whose messages are intercepted and processed by another
                      window procedure (or procedures) before being passed
                      to the window procedure of that class.

                      The SetWindowLong function creates the subclass by
                      changing the window procedure associated with a
                      particular window, causing Windows to call the new
                      window procedure instead of the previous one. Any
                      messages not processed by the new window procedure must
                      be passed to the previous window procedure by calling
                      CallWindowProc. This allows you to create a chain of
                      window procedures.


   Source code:       SOURCE\\WINAPI\\CallWnd.c

   See also:          SetWindowLong()