Asks to maximize window, so that it becomes full-screen. Note that you shouldn’t assume the window is definitely maximized afterward, because other entities (e.g. the user or [window manager][gtk-X11-arch]) could unmaximize it again, and not all window managers support maximization. But normally the window will end up maximized. Just don’t write code that crashes if not.
It’s permitted to call this function before showing a window, in which case the window will be maximized when it appears onscreen initially.