There is no way to create a group, what happens is just that relays (most likely when asked by users) will create rules around some specific ids so these ids can serve as an actual group, henceforth messages sent to that group will be subject to these rules.
Normally a group will originally belong to one specific relay, but the community may choose to move the group to other relays or even fork the group so it exists in different forms -- still using the same _id_ -- across different relays.
## Relay-generated events
Relays are supposed to generate the events that describe group metadata and group admins. These are parameterized replaceable events signed by the relay keypair directly, with the group _id_ as the `d` tag.
## The `h` tag
Events sent by users to groups (chat messages, text notes, moderation events etc) must have an `h` tag with the value set to the group _id_.
In order to not be used out of context, events sent to these groups may contain references to previous events seen from the same relay in the `previous` tag. The choice of which previous events to pick belongs to the clients.
This is a hack to prevent messages from being broadcasted to external relays that have forks of one group out of context. Relays are expected to reject any events that contain timeline references to events not found in their own database. Clients must also check these to keep relays honest about them.
Relays should prevent late publication (messages published now with a timestamp from days or even hours ago) unless they are open to receive a group forked or moved from another relay.
Clients can send these events to a relay in order to accomplish a moderation action. Relays must check if the pubkey sending the event is capable of performing the given action. The relay may discard the event after taking action or keep it as a moderation log.
This event defines the metadata for the group -- basically how clients should display it. It must be generated and signed by the relay in which is found. Relays shouldn't accept these events if they're signed by anyone else.
If the group is forked and hosted in multiple relays, there will be multiple versions of this event in each different relay and so on.
Each admin gets a label that is only used for display purposes, and a list of permissions it has are listed afterwards. These permissions can inform client building UI, but ultimately are evaluated by the relay in order to become effective.
The list of capabilities, as defined by this NIP, for now, is the following:
