@evan
Mastodon supports only a tiny subset of the ActivityPub vocabulary. (e.g. Post payload types are limited to either "Note" or "Question" (Poll).)
* Should new clients/services avoid ActivityPub vocabulary not supported by Mastodon?
* What are we missing as a result of Mastodon's incomplete support for the ActivityPub vocabulary?
* Is it useful to propose additional ActivityPub vocabulary if it isn't supported by Mastodon?
https://www.w3.org/TR/activitystreams-vocabulary/#object-types