code: func (base *Base) Writer(ctx context.Context, path string, append bool) (storagedriver.FileWriter, error) {
  	ctx, done := dcontext.WithTrace(ctx)
  	defer done("%s.Writer(%q, %v)", base.Name(), path, append)
  
  	if !storagedriver.PathRegexp.MatchString(path) {
  		return nil, storagedriver.InvalidPathError{Path: path, DriverName: base.StorageDriver.Name()}
  	}
  
  	writer, e := base.StorageDriver.Writer(ctx, path, append)
  	return writer, base.setDriverName(e)
  }
docs: // Writer wraps Writer of underlying storage driver.