Tags. We finally have tags.
I never really got perspectives, and contexts in OF 1 and 2. Or I understood them, but I never found a way to use them together in a prodctive way that made sense to me.
It took me a minute to get into perspectives with OF3.
My favourite thing about how tags are implemented though, is that you can use them like me as a flat structure, or like people used contexts in the past.