LINQ to XML:如何替换XCData的内容

using System;
using System.Linq;
using System.Xml.Linq;

namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
//写入CDATA元素块
var doc =
new XElement("Test",
new XElement("User",
new XAttribute("name", "chenxizhang"),
new XCData("这是XCData的内容，可以包含特殊字符，例如< 或者 >")));
Console.WriteLine("写入CData元素");
Console.WriteLine(doc.ToString());

Console.Write(doc.Element("User").Value);

}
}
}

.csharpcode, .csharpcode pre
{
font-size: small;
color: black;
font-family: consolas, "Courier New", courier, monospace;
background-color: #ffffff;
/*white-space: pre;*/
}
.csharpcode pre { margin: 0em; }
.csharpcode .rem { color: #008000; }
.csharpcode .kwrd { color: #0000ff; }
.csharpcode .str { color: #006080; }
.csharpcode .op { color: #0000c0; }
.csharpcode .preproc { color: #cc6633; }
.csharpcode .asp { background-color: #ffff00; }
.csharpcode .html { color: #800000; }
.csharpcode .attr { color: #ff0000; }
.csharpcode .alt
{
background-color: #f4f4f4;
width: 100%;
margin: 0em;
}
.csharpcode .lnum { color: #606060; }