void set_focus_chain(array widgets
Sets a focus chain, overriding the one computed automatically by GTK+.
In principle each widget in the chain should be a descendant of the
container, but this is not enforced by this method, since it's allowed
to set the focus chain before you pack the widgets, or have a widget
in the chain that isn't always packed. The necessary checks are done
when the focus chain is actually traversed.