Nevermind, I should've checked:

```sh
$ xp -r 'util.log.BoundLogObserver'
@FileSystemCL<...\xp.public\core\src\main\php\>
public interface util.log.BoundLogObserver extends util.Observer {
  rdbms.DBObserver instanceFor(var $arg)
  void update(util.Observable $obs, var $arg)
}
```