I was holding this back as out of scope and too close to the deadline, but now that we are talking about sliding windows and delayed, cached state, it is quite relevant.
This proposal uses HTTP caching algorithms, but does not require an HTTP transport. Atom over other transports can use these algorithms. <http://www.intertwingly.net/wiki/pie/PaceCaching> wunder -- Walter Underwood Principal Architect, Verity
