Define group rules and code of conduct

"As a fediverse user, I want to see a group's rules before joining or posting, so I know what behavior is expected."

Groups often have a code of conduct that users have to agree to before joining or participating. We propose standardising how rules are represented on Group actors for federation.

Existing approaches:

• Lemmy: Exposes community rules simply as a part of the summary text on the Group
• Mastodon: Instance-level rules are an array of objects with id and text

Suggested representation:

A rules property, supporting translations via the existing ActivityPub contentMap pattern:

{
  "type": "Group",
  "id": "https://example.org/groups/1",
  "rules": [
    {
      "mediaType": "text/html",
      "name": "Be respectful",
      "nameMap": {"fr": "Soyez respectueux"},
      "content": "<em>No personal attacks</em> or harassment.",
      "contentMap": {"fr": "Pas d'attaques personnelles ou de harcèlement."}
    },
    {
      "mediaType": "text/plain",
      "name": "Stay on topic",
      "nameMap": {"fr": "Restez dans le sujet"},
      "content": "Keep discussions related to the group's topic.",
      "contentMap": {"fr": "Gardez les discussions liées au sujet du groupe."}
    }
  ]
}

Translation pattern:

• name / content - Default language text (based on the community's primary language)
• nameMap / contentMap - Language-tagged alternatives (standard ActivityPub pattern, W3C Activity Streams *Map properties)
• Instances should display the user's preferred language if available, falling back to the default

Backwards compatibility:

• Implementations not understanding rules or the rule attachments simply ignore them
• Rules don't affect protocol behavior - they're informational only
• Existing summary field can include a link to a page that display the rules for simpler implementations

Open questions:

• Should we use attachment or the like (reusing existing AP vocabulary) vs dedicated rules property (cleaner but new)?
• Should rules be orderable (numbered)? Could use an OrderedCollection or just rely on array order
• Should rules have categories or severity levels?
• Should Flag activities reference which rule was violated?

Start by reviewing the existing ActivityPub Group vocabulary and the W3C Activity Streams natural-language *Map properties linked in the issue. Compare the Lemmy and Mastodon approaches, then resolve the attachment-versus-dedicated-property, ordering, and categorization questions. Done means the rules representation and compatibility behavior are specified clearly enough for implementations to follow.