xsl试图转换为另一个xsl样式表

Question

我试图在.net中进行xsl转换，输出另一个xsl样式表。我输出到文字看我正在建设。但是，我收到以下错误：

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Xml;
using System.Xml.Xsl;

namespace WebApplication1
{
    public partial class _default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            //http://stackoverflow.com/q/2384306/139698
            string transform = GetXsl();
            string input = GetXml();

            StringWriter sw = new StringWriter();
            using (XmlReader xrt = XmlReader.Create(new StringReader(transform)))
            using (XmlReader xri = XmlReader.Create(new StringReader(input)))
            using (XmlWriter xwo = XmlWriter.Create(sw))
            {
                XsltArgumentList xal = new XsltArgumentList();
                xal.AddExtensionObject(
                    MyXsltExtensionFunctions.Namespace,
                   new MyXsltExtensionFunctions());

                XslCompiledTransform xslt = new XslCompiledTransform();

                xslt.Load(xrt);

                xslt.Transform(xri, xal, xwo);
            }
            out11.InnerHtml = sw.ToString();
        }

        private string GetXml()
        {
            return
@"<?xml version='1.0' encoding='UTF-8'?>
<catalog>
    <data id='1' option1='key1' option2='0' />
    <data id='2' option1='' option2='1' />
</catalog>
";
        }

        private string GetXsl()
        {
            return
@"<?xml version='1.0' encoding='UTF-8'?>
    <xsl:stylesheet version='1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform' 
            xmlns:msxsl='urn:schemas-microsoft-com:xslt' exclude-result-prefixes='msxsl'
            xmlns:ext='http://XsltSampleSite.XsltFunctions/1.0'
            xmlns:xslout='blah'>

    <xsl:output method='text'/>

    <xslout:stylesheet version='1.0' xmlns:xsl='http://www.w3.org/1999/XSL/Transform'>

    <xsl:template match='/'>
        <span>
            <xsl:value-of select=""ext:HelloWorld()"" />
        </span>
     </xsl:template>
    </xslout:stylesheet>
</xsl:stylesheet>
";
        }
    }

    public class MyXsltExtensionFunctions
    {
        public const string Namespace = "http://XsltSampleSite.XsltFunctions/1.0";

        public string HelloWorld()
        {
            return "It works!";
        }
    }
}

以下是整个代码：

{{1}}