using System;

using System.Text.RegularExpressions;

​

public class Program

{

    public static void Main()

    {

        Regex regex = new Regex(@"<size(\s+)?=(\s+)?(.*)>", RegexOptions.Compiled);

        var match = regex.Match(@"<size=50>");

        if (!match.Success)

        {

            Console.WriteLine("Not matched!");

            return;

        }

​

        int groupIndex = 0;

        foreach (Group group in match.Groups)

        {

            Console.WriteLine("Group " + groupIndex + ". : " + group.Name);

            int captureIndex = 0;

            foreach (Capture capture in group.Captures)

            {

                Console.WriteLine("Capture " + captureIndex + ". : " + capture.Value);

                captureIndex++;

            }

            groupIndex++;

        }

    }

}