code: func normalizeKeys(key []string) {
  	for i, k := range key {
  		if !validCharactersRE.MatchString(k) {
  			// first replace */* with all
  			k = strings.Replace(k, allMatcher, allReplacement, -1)
  
  			// now replace all other invalid characters with a safe one.
  			key[i] = invalidCharactersRE.ReplaceAllString(k, normalizedToken)
  		}
  	}
  }
docs: // This function is used to make metric names safe for all metric services. Specifically, prometheus does
  // not support * or / in metric names.