gboolean gtk_widget_grab_focus ( GtkWidget* widget )
widget to have the keyboard focus for the
GtkWindow it’s inside.
widget is not focusable, or its
implementation cannot transfer the focus to a descendant of
that is focusable, it will not take focus and
FALSE will be returned.
gtk_widget_grab_focus() on an already focused widget
is allowed, should not have an effect, and return