The description should go to docs/dev/stream/state.md
Looks like some of the existing documentation got lost with 2fd543f80893ddd87eed773611fe7f23748008bb, e.g. the info about different state types and what they collect.
Additionally the following redirect is now failing:
title: "Working with State"
Implemented on master in :
Implemented on release-1.2 in: