Fullscreen window without Gnome Panel

[Vladislav Turbanov <vladipus yandex ru>]

I want to create a fullscreen window only using X11 functions. Everything works ok, but I get gnome panel appearing on top of my window, 
even if the window captures all of the user input. How can I programmatically hide the gnome panel, while still using only X11 functiions?
 Maybe there is some kind of hint for a window manager that can be passed from X11 to the window manager.