Comment 11 for bug 622718

just to straighten out on comment #8 - an achievement in g-a is either bronze, silver or gold [1]. the rank denotes the asserted difficulty to achieve the target or can be used to advertise the trophy as more valuable than other.
as not all achievements are of same difficulty or relevance, a rank makes sense. i believe you have the "priority" field for that

[1] as you can see in the actual use of the format:
http://github.com/tbaugis/gnome-achievements/blob/master/data/achievements/hamster-applet.trophies.xml