message: [data] Syncable interface must include `_sync`
diff: @@ -22,6 +22,8 @@ export interface Syncable {
  * of `Transform`s as an argument and applies it to the source.
  */
  sync(transformOrTransforms: Transform | Transform[]): Promise<void>;
  +
  + _sync(transform: Transform): Promise<void>;
  }
  /**
  