code: func OpenFilesForWriting(fs afero.Fs, filenames ...string) (io.WriteCloser, error) {
  	var writeClosers []io.WriteCloser
  	for _, filename := range filenames {
  		f, err := OpenFileForWriting(fs, filename)
  		if err != nil {
  			for _, wc := range writeClosers {
  				wc.Close()
  			}
  			return nil, err
  		}
  		writeClosers = append(writeClosers, f)
  	}
  
  	return hugio.NewMultiWriteCloser(writeClosers...), nil
  
  }
docs: // OpenFilesForWriting opens all the given filenames for writing.