Yelp (Gnome Help Center) is a Gnome application and as i mentioned earlier it follows Gnome 3 (Shell).Earlier versions of Yelp with Gnome 2 are obsolete packages ""untrusted archives"" : https://launchpad.net/ubuntu/+source/yelp
Gnome Flashback introduction in Yelp ? good point, this would have to be sugested to the developpers of
https://wiki.gnome.org/Projects/GnomeFlashback & Yelp
