From ac7add95447617ae541e1a9075091a6471afed4d Mon Sep 17 00:00:00 2001
From: a <a@trwnh.com>
Date: Fri, 9 Dec 2022 01:12:32 -0600
Subject: [PATCH] Add FEP-fb2a: Actor metadata

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+---
+authors: a <a@trwnh.com>
+status: DRAFT
+dateReceived: 2022-12-09
+---
+# FEP-fb2a: Actor metadata
+
+
+## Summary
+
+It is useful for actors to publish additional structured information about themselves without necessarily defining an extension property or additional vocabulary. This FEP describes a way for actors to publish generic key-value pairs representing their metadata.
+
+## History
+
+Mastodon v2.4.0 (March 2018) implemented "bio fields" [1], a feature that allows adding structured data to profiles. This feature was federated via the `attachment` field, filtering for array items that had a type of `PropertyValue` derived from schema.org's vocabulary. Each item used `name` from the ActivityStreams Vocabulary, and `value` from the schema.org context. The schema.org namespace was defined as `schema` and (erroneously) mapped to `http://schema.org#` (instead of `http://schema.org/` or `https://schema.org`) within the JSON-LD context property. 
+
+Misskey (December 2018) implemented "user fields" [2], following the same federation logic as Mastodon (filtering for a type of `PropertyValue`, then taking `name` and `value`).
+
+Pleroma (August 2019) implemented "custom profile fields" [3], following the same federation logic as Mastodon (filtering for a type of `PropertyValue`, then taking `name` and `value`).
+
+## 1. Using ActivityStreams Note instead of schema.org PropertyValue
+
+Rather than depending on an additional (and unnecessary) vocabulary, it makes sense to define a more "native" way of expressing the same idea of a key-value pair representing structured metadata about the actor. To this end, this FEP proposes using the existing `Note` type from the ActivityStreams 2.0 Vocabulary (instead of schema.org's `PropertyValue`), as well as the existing `content` property (instead of schema.org's `value`). Note that the `name` property exists within both the ActivityStreams 2.0 Vocabulary and the schema.org vocabulary, with largely the same semantic meaning; however, the use of schema.org vocabulary is out of scope of this FEP.
+
+Thus, we can define a standard for actor metadata, largely drawing from prior art.
+
+## 2. Defining actor metadata
+
+General-purpose actor metadata fields SHOULD be included in the `attachment` array on the actor. If a more specific property exists and is a better fit for the specific metadata being expressed, then implementations MAY use that instead of or in addition to the more generic actor metadata.
+
+- Each metadata field MUST have a type of `Note`.
+- Each metadata field MUST have a property of `name` representing the name (key) of the field.
+- Each metadata field MUST have a property of `content` representing the content (value) of the field.
+
+## 3. Backwards compatibility with legacy implementations
+
+(This section is non-normative.)
+
+Existing implementations currently using `http://schema.org#PropertyValue` and `http://schema.org#value` may wish to maintain backwards compatibility during a transitional period. The following algorithm may be used to support the legacy implementations while also favoring the implementation within this FEP:
+
+- Filter the `attachment` array for items of type `Note`. Take `name` and `content` from each remaining item.
+- If none are found, filter the `attachment` array for items of type `http://schema.org#PropertyValue`. Take `name` and `http://schema.org#value` from each remaining item.
+
+After some transitional period, implementations may wish to simplify their logic by filtering only for items of type `Note` and drop support for `http://schema.org#PropertyValue`, `http://schema.org#value`, and the schema.org context entirely (assuming those implementations do not use any other vocabulary from the schema.org context).
+
+## References
+
+- [ActivityPub] Christopher Lemmer Webber, Jessica Tallon, [ActivityPub](https://www.w3.org/TR/activitypub/), 2018
+- [1] Gargron, [Add bio fields (#6645)](https://github.com/mastodon/mastodon/pull/6645)
+- [2] mei23, [Show user fields (#3590)](https://github.com/misskey-dev/misskey/pull/3590)
+- [3] minibikini, [Add custom profile fields (!1488)](https://git.pleroma.social/pleroma/pleroma/-/merge_requests/1488)
+
+## Copyright
+
+CC0 1.0 Universal (CC0 1.0) Public Domain Dedication 
+
+To the extent possible under law, the authors of this Fediverse Enhancement Proposal have waived all copyright and related or neighboring rights to this work.