code: func isDestRelative(base, dest string) bool {
  	fullPath := dest
  	if !filepath.IsAbs(dest) {
  		fullPath = filepath.Join(base, dest)
  	}
  	relative, err := filepath.Rel(base, fullPath)
  	if err != nil {
  		return false
  	}
  	return relative == "." || relative == stripPathShortcuts(relative)
  }
docs: // isDestRelative returns true if dest is pointing outside the base directory,
  // false otherwise.