code: func (fs *languageCompositeFs) Open(name string) (afero.File, error) {
  	f, err := fs.CopyOnWriteFs.Open(name)
  	if err != nil {
  		return nil, err
  	}
  
  	fu, ok := f.(*afero.UnionFile)
  	if ok {
  		// This is a directory: Merge it.
  		fu.Merger = LanguageDirsMerger
  	}
  	return f, nil
  }
docs: // Open takes the full path to the file in the target filesystem. If it is a directory, it gets merged
  // using the language as a weight.