An application sends the WM_MDICASCADE message to a multiple document interface (MDI) client window to arrange all its child windows in a cascade format.
WM_MDICASCADE wParam = (WPARAM) (UINT) fuCascade; // cascade flag lParam = 0; // not used; must be zero
If the message succeeds, the return value is TRUE.
If the message fails, the return value is FALSE.