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WINDOW property which sets or gets the client window (not including title or status areas) messaging procedure for use with low-level Windows API calls that require it. Generally used with sub-classing to track all Windows messages.

**Example:**

**  PROGRAM**

**  MAP**

**   Main**

**   SubClassFunc(UNSIGNED hWnd,SIGNED wMsg,UNSIGNED wParam,LONG lParam),LONG,PASCAL**

**   MODULE('win32')                   !Windows Library**

**    CallWindowProc(LONG,UNSIGNED,SIGNED,UNSIGNED,LONG),LONG,PASCAL,NAME('CallWindowProcA')**

**   END**

**  END**

**SavedProc  LONG**

**PT     GROUP,PRE(PT)**

**X       SHORT**

**Y       SHORT**

**       END**

** CODE**

** Main**

** **

**Main          PROCEDURE**

**WinView WINDOW('View'),AT(0,0,320,200),HVSCROLL,MAX,TIMER(1)**

**         STRING('X Pos'),AT(1,1,,),USE(?String1)**

**         STRING(@n3),AT(24,1,,),USE(PT:X)**

**         STRING('Y Pos'),AT(44,1,,),USE(?String2)**

**         STRING(@n3),AT(68,1,,),USE(PT:Y)**

**         BUTTON('Close'),AT(240,180,60,20),USE(?Close)**

**        END**

** CODE**

** OPEN(WinView)**

** SavedProc = WinView{****PROP:ClientWndProc****}             !Save this procedure**

** WinView{PROP:ClientWndProc} = ADDRESS(SubClassFunc) !Change to subclass procedure**

** ACCEPT**

**  CASE ACCEPTED()**

**  OF ?Close**

**   BREAK**

**  END**

** END**

**SubClassFunc    PROCEDURE(hWnd,wMsg,wParam,lParam)   !Sub class procedure**

**WM_MOUSEMOVE    EQUATE(0200H)                        ! to track mouse movement in **

** CODE                                                ! client area of window**

** CASE wMsg**

** OF  WM_MOUSEMOVE**

**  PT:X = MOUSEX()**

**  PT:Y = MOUSEY()**

** END**

** RETURN(CallWindowProc(SavedProc,hWnd,wMsg,wParam,lParam)) **

**                                                     !Pass control back to**

**                                                     ! saved procedure**