How to use regular expression validation for value at user defined XPAth in XML file?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Text.RegularExpressions;

namespace yourprojectnamespace.subfoldername
{
    class DoCheckRegularExpression
    {
        public bool chkregularex(string User_defined_XPath, string User_defined_Xml_file, string User_defined_regularexpression)
        {
            bool val = false;
            
            try
            {
               
                XmlDocument xml_document = new XmlDocument();
                xml_document.Load(User_defined_Xml_file);
                XmlNodeList nodelist = xml_document.SelectNodes(User_defined_XPath);
                foreach (XmlNode node in nodelist)
                {
                    Regex pattern = new Regex(User_defined_regularexpression);
                    string[] outcome_reg_exp = node.InnerText.Trim().Split(new string[] { "\n", "\r\n" }, StringSplitOptions.RemoveEmptyEntries);
                    foreach (string s in outcome_reg_exp)
                    {
                        if (pattern.IsMatch(s))
                        {
                            val = true;
                            return val;
                        }
                        else
                        {
                            val = false;
                        }
                    }
                }

            
            }
            catch (XmlException)
            {
                System.Windows.Forms.MessageBox.Show("Please check XML file format" ,"XML file format exception");
               
            }
            return val;
        }
    }
}