code: func NewTagger(backend ImageComponent, stdout io.Writer, names []string) (*Tagger, error) {
  	reposAndTags, err := sanitizeRepoAndTags(names)
  	if err != nil {
  		return nil, err
  	}
  	return &Tagger{
  		imageComponent: backend,
  		stdout:         stdout,
  		repoAndTags:    reposAndTags,
  	}, nil
  }
docs: // NewTagger returns a new Tagger for tagging the images of a build.
  // If any of the names are invalid tags an error is returned.