matrix-spec/api/client-server/definitions/timeline_batch.json

{
  "type": "object",
  "allOf": [{"$ref":"event_batch.json"}],
  "properties": {
    "limited": {
      "type": "boolean",
      "description": "True if the number of events returned was limited by the ``limit`` on the filter"
    },
    "prev_batch": {
      "type": "string",
      "description": "If the batch was limited then this is a token that can be supplied to the server to retrieve earlier events"
    }
  }
}