js很有趣的问题？

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" >
<head>
    <title>未命名頁面</title>
    
    <script type="text/javascript">
    <!--
    var xmlhttp;
    
    function createHTTP()
    {
        if (window.ActiveXObject)
        {
            xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
        }
        else if (window.XMLHttpRequest)
        {
            xmlhttp = new XMLHttpRequest();
        }
    }
    
    function GetData()
    {
        createHTTP();
        xmlhttp.onreadystatechange = StateChange;
        xmlhttp.open("GET", "http://www.csdn.net", false);
        xmlhttp.send();
    }
    
    function StateChange()
    {
        if (xmlhttp.readystate == 4)
        {
            if (xmlhttp.status == 200)
            {
                document.getElementById('frame1').contentWindow.document.body.innerHTML = xmlhttp.responseText;
                document.getElementById('frame1').contentWindow.document.onmouseup = ShowSelection;
            }
        }
    }
    
    function ShowSelection()
    {
        var selection = document.getElementById('frame1').contentWindow.document.selection;
        document.getElementById('txtShow').value = selection.createRange().text;
    }
    
    //-->
    </script>
    
</head>
<body onload="GetData()">
    <input type="text" id="txtShow" style="width:400px" />
    <div>
        <iframe width="100%" height="100%" id="frame1">
        </iframe>
    </div>
</body>
</html>
大家有没有注意innerhtml读出来内容在子框架iframe中页面中出现乱码情况 
不知道怎么回事