How to serialize HtmlElement object in file stream??

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;
using System.Runtime.Serialization;
using System.Xml.Serialization;

namespace WindowsFormsApplication1
{
public partial class Form1 : Form
{
HtmlElement obj;
public Form1()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{

XmlSerializer sw = new XmlSerializer(typeof(HtmlElement ));
FileStream fs = new FileStream("1.txt", FileMode.OpenOrCreate);
sw.Serialize(fs, obj);
fs.Close();
}

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
HtmlElementCollection col = webBrowser1.Document.GetElementsByTagName("a");
foreach (HtmlElement htmlel in col)
{
if (htmlel != null)
{
obj = htmlel;
return;
}
}
}

private void Form1_Load(object sender, EventArgs e)
{
webBrowser1.Navigate("www.digg.com");
}
}
}


please see the code.

i am getting error....
System.Windows.Forms.HtmlElement cannot be serialized because it does not have a parameterless constructor.