javascript基础

<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/xml; charset=UTF-8">
</head>
<body>
<script type="text/javascript">
function createDocument() {
        if(typeof arguments.callee.activeXString !="string") { var versions = ["MSXML2.DOMDocument.6.0","MSXML2.DOMDocument.3.0","MSXML2.DOMDocument"];      for(var i=0,len=versions.length;i<len;i++) { try { var xmldom = new ActiveXObject(version[i]);
arguments.callee.activeXString = version[i];
return xmldom; }catch(ex) {                                    //版本无效
} }
} return new ActiveXObject(arguments.callee.activeXString);//类型不匹配
} var xmldom = createDocument();
xmldom.loadXML("<root><child/></root>"); alert(xmldom.documentElement.tagName);
alert(xmldom.documentElement.firstChild.tagName);
</script>
"return new ActiveXObject(arguments.callee.activeXString);"出现类型不匹配错误是怎么回事？