Slop.

Someone in a different release thread was going on about how piefed just made up its own federation return ignoring standards

Found it

https://lemmy.world/comment/21179968

Edit, for those getting wrong thread comment in question

It's this kind of thinig that makes me think of PieFed as just a pile of hacks with no serious consideration for the Fediverse

Designating which comment is an answer involves federating a new Activity:

{  
         "id": "https://piefed.social/activities/answer/hgb4iO4b8UAFRTn", 
         "type": "ChooseAnswer",  
         "actor": "https://piefed.socialz/u/rimu", 
         "object": "https://piefed.ngrok.app/comment/224",  
         "@context": ["https://www.w3.org/ns/activitystreams", "https://w3id.org/security/v1"],  
         "audience": "https://crust.piefed.social/c/linux_questions",  
         "to": ["https://www.w3.org/ns/activitystreams#Public"],  
         "cc": ["https://crust.piefed.social/c/linux_questions"]  
}  

There are at least three different ways to implement this in a way compatible with ActivityPub:

1. Send an "as:accept" activity with the comment as the object.

2. Add an attribute for the comment indicating that it has been selected.

3. Create a collection for chosen answers, add to the post object.

And even if this type of new activity was a necessity, they could add their own extensions via a proper JSON-LD context definition. But they completely disregard JSON-LD, which means that they expect other servers to either (1) adopt their ad-hoc vocabulary or (2) ignore it completely and keep this idea that "Only PieFed has these features".