public Tag Parse(string tag, string value)
        {
            PolicyType policyType;

            if (!value.TryParseExactEnum(out policyType))
            {
                policyType = PolicyType.Unknown;
            }

            Policy policy = new Policy(tag, policyType);

            if (policyType == PolicyType.Unknown)
            {
                string errorMessage = string.Format(DmarcParserResource.InvalidValueErrorMessage, Tag, value);
                policy.AddError(new Error(ErrorType.Error, errorMessage));
            }

            return(policy);
        }