In a chat room info page, users can be sorted according to "frequently in room". What does this order actually do?
This is how it currently works:
There's no guarantee this formula won't ever change, but it's been like this for a while, and its results are usually pretty good.
It's not so much sort order, as it is more primarily a listing. It says in the tooltip:
As such, to differentiate it from "currently in room", it can include users who are not physically present at the immediate moment, yet are constant contributors.
I imagine it's sorted in some rough fashion based on that level of activity, the most active such users being listed at the top. This is probably based on activity time moreso than post count.