AjaxControlToolkit.HtmlEditor.Sanitizer.DefaultHtmlSanitizer.EncodeCharacterToHtmlEntityEscape C# (CSharp) Method

        static string EncodeCharacterToHtmlEntityEscape(char c)
        {
            // check for illegal characters
            if((c <= 31 && c != '\t' && c != '\n' && c != '\r') || (c >= 127 && c <= 159))
                return "&#xfffd;"; // Let's entity encode this instead of returning it
            else
                return c.ToString();
        }