code: func rootedIn(root string, parts []string) string {
  	//log.Printf("rootIn(%s, %v)", root, parts)
  	for i := 1; i < len(parts); i++ {
  		suffix := filepath.Join(parts[i:]...)
  		if isFile(filepath.Join(root, suffix)) {
  			return filepath.Join(parts[:i]...)
  		}
  	}
  	return ""
  }
docs: // rootedIn returns a root if the file split in parts is rooted in root.