code: func NewDefaultCamliFileSystem(client *client.Client, fetcher blob.Fetcher) *CamliFileSystem {
  	if client == nil || fetcher == nil {
  		panic("nil argument")
  	}
  	fs := newCamliFileSystem(fetcher)
  	fs.root = &root{fs: fs} // root.go
  	fs.client = client
  	return fs
  }
docs: // NewDefaultCamliFileSystem returns a filesystem with a generic base, from which
  // users can navigate by blobref, tag, date, etc.