code: func baseDomain(name string) string {
  	eTLDPlusOne, err := publicsuffix.Domain(name)
  	if err != nil {
  		// publicsuffix.Domain will return an error if the input name is itself a
  		// public suffix. In that case we use the input name as the key for rate
  		// limiting. Since all of its subdomains will have separate keys for rate
  		// limiting (e.g. "foo.bar.publicsuffix.com" will have
  		// "bar.publicsuffix.com", this means that domains exactly equal to a
  		// public suffix get their own rate limit bucket. This is important
  		// because otherwise they might be perpetually unable to issue, assuming
  		// the rate of issuance from their subdomains was high enough.
  		return name
  	}
  	return eTLDPlusOne
  }
docs: // baseDomain returns the eTLD+1 of a domain name for the purpose of rate
  // limiting. For a domain name that is itself an eTLD, it returns its input.