@guppegroups Could you please change the link from lemmy.ml to join-lemmy.org? The former is just one instance of many, and we dont want everyone to signup there.
@datatitian@activitypub To post in a Lemmy community, you mainly need to include its id in the to/cc field. This works from most platforms including Mastodon. Replies to posts appear on Lemmy automatically, but you should again put the community it in to/cc. Other than that you can also like/dislike, follow communities and more.
@delta Activitypub is based on json, so you can add as much extra data as you want even if its not mentioned in the standard. Only problem is that other platforms would not necessarily understand it.
As you mention Rust, I am currently working on a major update for the activitypub-federation crate which improves usability and documentation. I will publish a release candidate in the next days.