Gtk.Window.prototype.set_title

function set_title(title:String):void {
    // Gjs wrapper for gtk_window_set_title()
}

Sets the title of the Gtk.Window. The title of a window will be displayed in its title bar; on the X Window System, the title bar is rendered by the <link linkend="gtk-X11-arch">window manager</link>, so exactly how the title appears to users may vary according to a user's exact configuration. The title should help a user distinguish this window from other windows they may have open. A good title might include the application name and current document filename, for example.