code: func suffixesForRateLimiting(names []string) ([]string, error) {
  	var suffixMatches []string
  	for _, name := range names {
  		_, err := publicsuffix.Domain(name)
  		if err != nil {
  			// Like `domainsForRateLimiting`, the only possible errors here are:
  			// (1) publicsuffix.Domain is giving garbage values
  			// (2) the public suffix is the domain itself
  			// We assume 2 and collect it into the result
  			suffixMatches = append(suffixMatches, name)
  		}
  	}
  	return core.UniqueLowerNames(suffixMatches), nil
  }
docs: // suffixesForRateLimiting returns the unique subset of input names that are
  // exactly equal to a public suffix.