using System;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string source_small = @"<ol><li>asdsklfdjs</li></ol>";

        string source = @"<b>Some Initial Content was in this textarea</b><div><b><i>test</i></b></div><div>test</div><div><u>test</u></div><div><u><br></u></div><div><ol><li><u>fdsklfdjs</u></li><li><u>fdjklfdjlfjs</u></li><li><u>fdsjklkfjdslfjds</u></li><li><u>fdjslkfjdslfjdslfds</u></li><ol><li><u>flkdsjflkdsjlfds</u></li><li><u>fdsjlfsdjlfdsjlfds</u></li><li><u>fsdjlkfdsjlfdsjlfds</u></li><li><u>jfdsljfdskljfdlsfds</u></li><ol><li><u>djsklfdsjlfjsd</u></li><li><u>fsdjlklkfsdjsldf</u></li><li><u>fdsjkllfsdjflsd</u></li><ul><li><u>fdsflkdsjflds</u></li><li><u>fdsljkfsdjlfsd</u></li><li><u>fdsjlfsdjfds</u></li><li><u>fdslkjfdslfdsl</u></li><ul><li><u>fdkjslfdjlfjs</u></li><li><u>fdsjlfldsjflsdj</u></li><li><u>fsdjlfjsdfsdjl</u></li></ul><li><u>dsjlfdjsfjlsdfsjflkldsjflsd</u></li><li><u>fdsjlfsd</u></li><li><u>fdsjlkfsdjlfsfdsj</u></li></ul><li><u>fjdslfkjsdjfsld</u></li><li><u>fsldjfdskljfsdl</u></li></ol><li><u>fdjslfdjslfsdj</u></li></ol><li><u>jldfsjfdslfjldfsjfds</u></li><li><u>fdsjlfjdslfjdsfjsdl</u></li><li><u>fjdsljfkdsljfkldsjfdsl</u></li></ol><div><u><br></u></div></div><div><u>fsdjlkfjdslfjdslfjdslkjfldksjflsd</u></div>";

        Console.WriteLine(StripULList(StripOLList(source_small)));

    }

    private static string StripOLList(string source)

        {

            string output = "";

            try

            {                

                string patternOL = @"<(ol)\s[^\>]*>(<li>.*?</li>)+?</\1>";                

                string trg = Regex.Replace(source, patternOL, (param) =>

                {                    

                    if (param.Groups[1].Value.Equals("ol"))

                    {

                        int i = 1;

                        foreach (Capture c in param.Groups[2].Captures)

                            output += String.Format("{0}. {1}\n", i++, Regex.Replace(c.Value, "<li>(.*?)</li>", "$1"));

                    }                    

                    return output;

                });                

                return trg;                

            }

            catch

            {

                return source;

            }

        }

​

​

private static string StripULList(string source)

        {

            string output = "";

            try

            {

                string patternUL = @"<(ul)\s[^\>]*>(<li>.*?</li>)+?</\1>";                

                string trg = Regex.Replace(source, patternUL, (param) =>

                {

                    if (param.Groups[1].Value.Equals("ul"))

                    {

                        foreach (Capture c in param.Groups[2].Captures)

                            output += String.Format("{0} {1}\n", "-", Regex.Replace(c.Value, "<li>(.*?)</li>", "$1"));

                    }                    

                    return output;

                });                

                return trg;                

            }

            catch

            {

                return source;

            }

        }

}