window-system-version on Windows

[Juanma Barranquero]

Why is Fwindow_system_version initialized to 1 on dispnew.c

  #ifdef HAVE_NTGUI
    if (!inhibit_window_system)
      {
        Vinitial_window_system = intern ("w32");
        Vwindow_system_version = make_number (1);
        adjust_frame_glyphs_initially ();
        return;
      }
  #endif /* HAVE_NTGUI */

and then unconditionally set to 3

  XSETFASTINT (Vwindow_system_version, 3);

at two places of w32fns.c (x_display_info_for_name and Fx_open_connection)?

Also, what is its meaning on Windows? What does the 3 stands for?

    Juanma