WM_NEXTDLG
  This message is sent to a dialog box's window function, to alter the con-
trol focus.

Parameters
  wParam - If the lParam parameter is nonzero, the wParam parameter iden-
           tifies the control that receives the focus. If lParam is zero,
           wParam is a flag that indicates whether the next or previous
           control with tab-stop style receives the focus. If wParam is
           zero, the next control receives the focus; otherwise, the
           previous control with tab-stop style receives the focus.

  lParam - Contains a flag that indicates how Windows uses the wParam
           parameter. If the lParam parameter is nonzero, wParam is a
           handle associated with the control that receives the focus;
           otherwise, wParam is a flag that indicates whether the next or
           previous control with tab-stop style receives the focus.




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