BOOL CALLBACK DismissOwnedPopups(HWND window, LPARAM arg) {
  const HWND toplevel_hwnd = reinterpret_cast<HWND>(arg);

  if (::IsWindowVisible(window)) {
    const HWND owner = ::GetWindow(window, GW_OWNER);
    if (toplevel_hwnd == owner) {
      ::PostMessage(window, WM_CANCELMODE, 0, 0);
    }
  }

  return TRUE;
}

Unknown