code: func Rel(basepath containerfs.ContainerFS, targpath string) (string, error) {
  	// filepath.Rel can't handle UUID paths in windows
  	if basepath.OS() == "windows" {
  		pfx := basepath.Path() + `\`
  		if strings.HasPrefix(targpath, pfx) {
  			p := strings.TrimPrefix(targpath, pfx)
  			if p == "" {
  				p = "."
  			}
  			return p, nil
  		}
  	}
  	return basepath.Rel(basepath.Path(), targpath)
  }
docs: // Rel makes a path relative to base path. Same as `filepath.Rel` but can also
  // handle UUID paths in windows.