I notice that a reference to GtkStrengthBar had been left in this file when it was renamed to GtkLevelBar. On closer inspection, it looks like it's been unused for 13 years. To quote docs/reference/ChangeLog: > 2000-10-23 Havoc Pennington <hp@redhat.com> > > [...] Removed objects_grouped.sgml from gtk-docs.sgml for now, it > doesn't seem useful anymore. https://bugzilla.gnome.org/show_bug.cgi?id=700575