@fediversereport
I think all of the editors and authors of ActivityPub and Activity Streams in the previous iteration of the working group were "invited experts", except one (@jasnell ). One of the chairs (me) was as an invited expert.
The chairs (@tantek.com , @lehors and I) had a "knock to get invited" policy: anyone who expressed interest in participating in the working group was invited to join. I can't remember a situation where we turned someone down.