matrix-doc/event-schemas/examples/core/room_event.json

{
    "$ref": "event.json",
    "event_id": "$143273582443PhrSn:example.org",
    "room_id": "!jEsUZKDJdhlrceRyVU:example.org",
    "sender": "@example:example.org",
    "origin_server_ts": 1432735824653,
    "unsigned": {
      "age": 1234
    }
}