The Custom Emojis extension allows users to create and publish “emoji packs,” which are sets of small images that can then be included inline in notes (- and other locations??? bio, display name?). Emoji packs and the emojis contained within are identified by a globally unique ID (what kind? uuid?? does it even need this???) along with the usual object URI, allowing them to be cloned to multiple instances if desired without duplication (though this is not necessary, and a user from any instance can use emojis from any other instance).
These are extension objects.
TODO