using System;

using System.Xml;

public class Program

{

    public static void Main()

    {

        // This XML contains special characters that need to be escaped in attributes and node content

        string xmlText = "<root><AccountRef name=\"NW Op - M&T BANK #123456\" alias=\"M&T BANK\">99&B</AccountRef><AccountRef name=\"NW Op - M&T BANK #123456\"><SubData>99-B&100-B>2</SubData></AccountRef></root>";

​

        try

        {

            Console.WriteLine("Original XML:");

            Console.WriteLine(xmlText);

            // Escape attributes and node content

            string wellFormedXml = EscapeAttributesAndNodeValues(xmlText);

            Console.WriteLine("\nEscaped XML:");

            Console.WriteLine(wellFormedXml);

            // Load the escaped XML into an XmlDocument

            XmlDocument xmlDoc = new XmlDocument();

            xmlDoc.LoadXml(wellFormedXml);

            Console.WriteLine("\nValid XML 🥳.");

        }

        catch (XmlException ex)

        {

            Console.WriteLine($"\nInvalid XML 😞: {ex.Message}");

        }

    }

    // Function to escape special XML characters in attributes and node values

    static string EscapeAttributesAndNodeValues(string xml)

    {

        // Escape attributes (handling multiple attributes per tag)

        var result = System.Text.RegularExpressions.Regex.Replace(xml,

            @"(\w+\s*=\s*"")([^""]*)(""\s*)",

            m => $"{m.Groups[1].Value}{EscapeXmlCharacters(m.Groups[2].Value)}{m.Groups[3].Value}");

​

        // Escape node content values (text between tags)

        result = System.Text.RegularExpressions.Regex.Replace(result,

            @">(.*?)<",

            m => $">{EscapeXmlCharacters(m.Groups[1].Value)}<");

​

        return result;

    }

​

    // Function to escape special XML characters

    static string EscapeXmlCharacters(string value)

    {

        var result = value.Replace("&", "&")

                          .Replace("<", "&lt;")

                          .Replace(">", ">")

                          .Replace("\"", """)

                          .Replace("'", "'");

        return result;

    }

}

​