code: func (d *Differ) Diff(obj Object, printer Printer) error {
  	if err := d.From.Print(obj, printer); err != nil {
  		return err
  	}
  	if err := d.To.Print(obj, printer); err != nil {
  		return err
  	}
  	return nil
  }
docs: // Diff diffs to versions of a specific object, and print both versions to directories.