Good morning. The sun is shining and I got blue sky! Not the one one needs an invite for, don't worry.
Anyway, I feel like pointing out another flaw in the ActivityPub Specification, there are parts that are not abstract enough, e.g. explicitly telling us to use HTTP for communication, and there are parts that are too abstract, e.g. not explaining what an ActivityPub Server or an ActivityPub Client is. I've just searched and this is the only hit for 'ActivityPub server'. This makes me smile a lot.
Now the question: Is Mastodon an ActivityPub Server? Or is Mastodon an ActivityPub Server/Client combination that implements the entire specification?
Answer: You cannot decide. In order to answer the question, you need to formulate your guess what the words mean first. Depending on your meaning, the answers are yes or no.


