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It won't; you'll have to construct the list yourself, along the lines
of:

           List<string> l = new List<string>();
           foreach (Match m in Regex.Matches(s, "http://[0-9?&a-z-_./]
+", RegexOptions.Singleline)) {
               l.Add(m.Value);
           }

This uses the static method Regex.Matches, which essentially
constructs a RegEx instance and discards it after finding the matches.
You might want to reuse the RegEx instance for performance reasons.