code: func ResourceKeyPartition(filename string) string {
  	ext := strings.TrimPrefix(path.Ext(filepath.ToSlash(filename)), ".")
  	if ext == "" {
  		ext = CACHE_OTHER
  	}
  	return ext
  }
docs: // ResourceKeyPartition returns a partition name
  // to  allow for more fine grained cache flushes.
  // It will return the file extension without the leading ".". If no
  // extension, it will return "other".