code: func ExtractTag(path string) string {
  	match := tagExp.FindStringSubmatch(path)
  	// match is []string{"whole match", "submatch"} when successful
  
  	if len(match) != 2 {
  		return ""
  	}
  	return match[1]
  }
docs: // Returns the tag from a filename, whether at the end or middle.