crystallizing the thought that the "activitypub network" is anything that publishes activities, so in other words, anything with an outbox

but not every part of the network understands the same things, and some of them bypass the outbox, so we really have 3 distinct senses of "activitypub":

- activitypub via outbox, almost direct lineage from atom feeds or rss channels
- activitypub via inbox, a specialization of ldn
- activitypub via http, where you GET http resources with Content-Type of AS2