Remarks
Contains a pointer to the CWnd object for which dialog data exchange (DDX) or validation (DDV) is taking place. This object is usually a CDialog object. Implementors of custom DDX or DDV routines can use this pointer to obtain access to the dialog window that contains the controls they are operating on.
For more information on writing your own DDX and DDV routines, see Technical Note 26. For an overview of DDX and DDV, see Dialog Data Exchange and Validation and Dialog Box Topics in Visual C++ Programmer's Guide.