How to use this forum - Tips and Tricks

More of question than a tip or trick: what do the the mini avatars in the thread lists mean? I think it something like: “the OP on the left, followed by avatars of the latest posters, with the most recent one who is not the OP on the right, and if the OP recently participated put a little halo around that avatar”. Is that it?

Recent example from the e-ink thread:
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