matrix-spec-proposals/event-schemas/schema/v1/core-event-schema/room_event.json

{
  "type": "object",
  "title": "Room Event",
  "description": "In addition to the Event fields, Room Events MUST have the following additional field.",
  "allOf":[{
    "$ref": "core-event-schema/event.json"
  }],
  "properties": {
    "room_id": {
      "type": "string",
      "description": "The ID of the room associated with this event."
    },
    "event_id": {
      "type": "string",
      "description": "The globally unique event identifier."
    },
    "user_id": {
      "type": "string",
      "description": "Contains the fully-qualified ID of the user who *sent* this event."
    }
  },
  "required": ["room_id"]
}