Sim/operation/windows/system window

From X-Plane SDK

This is a handle to the OS's native window that X-Plane is running in.

On Macintosh:

This is a WindowRef stuffed in an int.

On Windows:

This is a windows HANDLE stuffed in an int.

On Linux:

On Linux this dataref is not set

For example:

XPLMDataRef	winRef = XPLMFindDataRef("sim/operation/windows/system_window");
if (winRef)
{
    WindowRef win = (WindowRef) XPLMGetDatai(winRef);
    Rect	foo = { 0, 0, 768, 1024 };
    InvalWindowRect(win, &foo);
    XPLMDebugString("Invalidating window.\n");
}

Note: this code is not really a good idea - I only post it for demonstration purposes.