matrix-spec-proposals/content/client-server-api/modules/moderation_policies.md

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Moderation policy lists

With Matrix being an open network where anyone can participate, a very wide range of content exists and it is important that users are empowered to select which content they wish to see, and which content they wish to block. By extension, room moderators and server admins should also be able to select which content they do not wish to host in their rooms and servers.

The protocol's position on this is one of neutrality: it should not be deciding what content is undesirable for any particular entity and should instead be empowering those entities to make their own decisions. As such, a generic framework for communicating "moderation policy lists" or "moderation policy rooms" is described. Note that this module only describes the data structures and not how they should be interpreting: the entity making the decisions on filtering is best positioned to interpret the rules how it sees fit.

Moderation policy lists are stored as room state events. There are no restrictions on how the rooms can be configured (they could be public, private, encrypted, etc).

There are currently 3 kinds of entities which can be affected by rules: user, server, and room. All 3 are described with m.policy.rule.<kind> state events. The state_key for a policy rule is an arbitrary string decided by the sender of the rule.

Rules contain recommendations and reasons for the rule existing. The reason is a human-readable string which describes the recommendation. Currently only one recommendation, m.ban, is specified.

m.ban recommendation

When this recommendation is used, the entities affected by the rule should be banned from participation where possible. The enforcement of this is deliberately left as an implementation detail to avoid the protocol imposing its opinion on how the policy list is to be interpreted. However, a suggestion for a simple implementation is as follows:

• Is a user rule...
  • Applied to a user: The user should be added to the subscriber's ignore list.
  • Applied to a room: The user should be banned from the room (either on sight or immediately).
  • Applied to a server: The user should not be allowed to send invites to users on the server.
• Is a room rule...
  • Applied to a user: The user should leave the room and not join it (MSC2270-style ignore).
  • Applied to a room: No-op because a room cannot ban itself.
  • Applied to a server: The server should prevent users from joining the room and from receiving invites to it.
• Is a server rule...
  • Applied to a user: The user should not receive events or invites from the server.
  • Applied to a room: The server is added as a denied server in the ACLs.
  • Applied to a server: The subscriber should avoid federating with the server as much as possible by blocking invites from the server and not sending traffic unless strictly required (no outbound invites).

Subscribing to policy lists

This is deliberately left as an implementation detail. For implementations using the Client-Server API, this could be as easy as joining or peeking the room. Joining or peeking is not required, however: an implementation could poll for updates or use a different technique for receiving updates to the policy's rules.

Sharing

In addition to sharing a direct reference to the room which contains the policy's rules, plain http or https URLs can be used to share links to the list. When the URL is approached with a Accept: application/json header or has .json appended to the end of the URL, it should return a JSON object containing a room_uri property which references the room. Currently this would be a matrix.to URI, however in future it could be a Matrix-schemed URI instead. When not approached with the intent of JSON, the service could return a user-friendly page describing what is included in the ban list.

Events

The entity described by the state events can contain * and ? to match zero or more and one or more characters respectively. Note that rules against rooms can describe a room ID or room alias - the subscriber is responsible for resolving the alias to a room ID if desired.

{{m_policy_rule_user_event}}

{{m_policy_rule_room_event}}

{{m_policy_rule_server_event}}

Client behaviour

As described above, the client behaviour is deliberately left undefined.

Server behaviour

Servers have no additional requirements placed on them by this module.

Security considerations

This module could be used to build a system of shared blacklists, which may create a divide within established communities if not carefully deployed. This may well not be a suitable solution for all communities.

Depending on how implementations handle subscriptions, user IDs may be linked to policy lists and therefore expose the views of that user. For example, a client implementation which joins the user to the policy room would expose the user's ID to observers of the policy room. In future, MSC1228 and MSC1777 (or similar) could help solve this concern.