using System;

using System.IO;

using System.Xml;

​

namespace Demo {

   class Program {

       public static (bool, XmlException?) IsvalidXml(string xml)

       {

           try

           {

               using var reader = new StringReader(xml);

               using var xmlReader = XmlReader.Create(reader, new XmlReaderSettings { ConformanceLevel = ConformanceLevel.Auto });

​

               while (xmlReader.Read());

           }

           catch (XmlException exception)

           {

               return (false, exception);

           }

​

           return (true, null);

       }

       static void Main(string[] args) {

           var (v, e) = IsvalidXml("<Tag>x=y&z=w</Tag>");

           Console.WriteLine(v ? "true" : "false");

           Console.WriteLine(e?.Message);

       }

   }

}