Check for XML encoded chars

EscapedAmpersand.cs

        public static ValidationResult EscapedAmpersand(string sampleStr)
        {
            Regex specChar = new Regex(@"&(?!(?:apos|quot|[A-Za-z0-1!?.,\ -]|amp);|#)", RegexOptions.IgnoreCase);
            MatchCollection matches = specChar.Matches(sampleStr);

            if (matches.Count > 0)
            {
                return new ValidationResult("Message cannot contain special characters.");
            }
            return ValidationResult.Success;

        }