matrix-doc/event-schemas/examples/m.room.message$m.text

{
  "$ref": "core/room_event.json",
  "type": "m.room.message",
  "content": {
    "body": "This is an example text message",
    "msgtype": "m.text",
    "format": "org.matrix.custom.html",
    "formatted_body": "<b>This is an example text message</b>"
  }
}