Fediverse

@nutomic

Do you know how this kind of federated community search is implemented in terms of Activitypub?

In case you meant me:
Hubzilla has its own protocol (Zot) and network, but is interoperable with most of the AP network. But the federated search is implemented by searching the public channels on public instances registered in directory servers (i.e. that want to be found), which is implemented only in Hubzilla servers, so AFAIK, AP contacts have to be entered explicitly by their webbie, instead. The directory servers (I am aware of four) are synchronized, so they are redundant.

In (streams), AFAIK this was changed to a more implicit search that browses the instances of your ID's contacts (and contacts of contacts, to a configurable depths - which makes it more decentral, but also more context-/channel-dependent, and consumes more capacity than browsing a central register).

This search is highly configurable and integrated into the apps' UI. So you just search from your channel's interface, and click "add as contact" (which includes group channels => like "subscribe to community").