code: def annotate_mapper(**decargs):
      
      def decorator(func):
          """Annotate events with entry and/or exit timestamps."""
          def wrapper(event, *args, **kwargs):
              """Add enter and exit annotations to the processed event."""
              funcname = ":".join([func.__module__, func.__name__])
              enter_ts = time.time()
              out = func(event, *args, **kwargs)
              enter_key = funcname + "|enter"
              out = annotate_event(out, enter_key, ts=enter_ts, **decargs)
              exit_key = funcname + "|exit"
              out = annotate_event(out, exit_key, ts=time.time(), **decargs)
              return out
  
          return wrapper
      return decorator
docs: Add input and output watermarks to processed events.