[yt-dev] strict and unstrict regions, periodic regions

HI all, Can someone remind me why we need the strict and unstrict region objects? The strict ones select by cell center, the unstrict by any intersection. I seem to recall a concrete use case but I can't dredge it up. Additionally, if we are actually checking for periodicity, it seems to me we have no need for non-periodic regions, right? We just coalesce into a single rectangular prism object that, if appropriate for the simulation, wraps around? -Matt