code: func SHA1DeprecationMessages(chain []*x509.Certificate) []string {
  	// record the most severe deprecation policy by each platform
  	selectedPolicies := map[string]SHA1DeprecationPolicy{}
  	for _, policy := range SHA1DeprecationPolicys {
  		if policy.Flag(chain) {
  			// only keep the policy with highest severity
  			if selectedPolicies[policy.Platform].Severity < policy.Severity {
  				selectedPolicies[policy.Platform] = policy
  			}
  		}
  	}
  	// build the message list
  	list := []string{}
  	for _, policy := range selectedPolicies {
  		if policy.Severity > None {
  			list = append(list, fmt.Sprintf("%s %s due to SHA-1 deprecation", policy.Platform, policy.Description))
  		}
  	}
  	return list
  }
docs: // SHA1DeprecationMessages returns a list of human-readable messages. Each message describes
  // how one platform rejects the chain based on SHA1 deprecation policies.