2022-06-22 UTC
# 
@bcjbcjbcj ↩️ apparently, every time I've looked at the activitypub spec it looked like messages were designed with like 5 different purposes in mind.
Not where it's definited, but here's a mention of it in an example:
https://www.w3.org/TR/activitypub/#client-to-server-interactions (twitter.com/_/status/1539689330402242560)