matrix-spec/data/event-schemas/examples/m.room.topic.yaml

{
  "$ref": "core/state_event.json",
  "type": "m.room.topic",
  "state_key": "",
  "content": {
    "m.topic": {
      "m.text": [ {
        "mimetype": "text/html",
        "body": "An <em>interesting</em> room topic"
      }, {
        "body": "An interesting room topic"
      }]
    },
    "topic": "An interesting room topic"
  }
}