code: func libraryPath(l *library.Library, id string) string {
  	// DatastoreID (moref) format is "$local-path@$ds-folder-id",
  	// see simulator.HostDatastoreSystem.CreateLocalDatastore
  	ds := strings.SplitN(l.Storage[0].DatastoreID, "@", 2)[0]
  	return path.Join(append([]string{ds, "contentlib-" + l.ID}, id)...)
  }
docs: // libraryPath returns the local Datastore fs path for a Library or Item if id is specified.