If @focus is not the current focus widget, and is focusable,
sets it as the focus widget for the window. If @focus is %NULL,
unsets the focus widget for this window. To set the focus to a
particular widget in the toplevel, it is usually more convenient
to use [method@Gtk.Widget.grab_focus] instead of this function.
Sets the focus widget.
If @focus is not the current focus widget, and is focusable, sets it as the focus widget for the window. If @focus is %NULL, unsets the focus widget for this window. To set the focus to a particular widget in the toplevel, it is usually more convenient to use [method@Gtk.Widget.grab_focus] instead of this function.