提供一个跨浏览器的XML DOM对象解决方案，来自于《javascript高级程序设计》

function XmlDom() {
//通过对象/属性检测法，判断是IE来是Mozilla
if (window.ActiveXObject) {
var arrSignatures = ["MSXML2.DOMDocument.5.0", "MSXML2.DOMDocument.4.0",
"MSXML2.DOMDocument.3.0", "MSXML2.DOMDocument",
"Microsoft.XmlDom"];
for (var i=0; i < arrSignatures.length; i++) {
try {
var oXmlDom = new ActiveXObject(arrSignatures[i]);
return oXmlDom;
            } catch (oError) {
//ignore
            }
        }         
throw new Error("MSXML is not installed on your system.");
//同上         
    } else if (document.implementation && document.implementation.createDocument) {
var oXmlDom = document.implementation.createDocument("","",null);
//创建Mozilla版本的parseError对象
        oXmlDom.parseError = {
            valueOf: function () { return this.errorCode; },
            toString: function () { return this.errorCode.toString() }
        };
//初始化parseError对象
        oXmlDom.__initError__();
        oXmlDom.addEventListener("load", function () {
this.__checkForErrors__();
this.__changeReadyState__(4);
        }, false);
return oXmlDom;       
    } else {
throw new Error("Your browser doesn't support an XML DOM object.");
    }
}
//此处用到了该书中一个浏览器系统检测js文件，如果是Mozilla
if (isMoz) {
    Document.prototype.readyState = 0;
    Document.prototype.onreadystatechange = null;
    Document.prototype.__changeReadyState__ = function (iReadyState) {
this.readyState = iReadyState;
if (typeof this.onreadystatechange == "function") {
this.onreadystatechange();
        }
    };
//初始化parseError对象
    Document.prototype.__initError__ = function () {
this.parseError.errorCode = 0;
this.parseError.filepos = -1;
this.parseError.line = -1;
this.parseError.linepos = -1;
this.parseError.reason = null;
this.parseError.srcText = null;
this.parseError.url = null;
    };
    Document.prototype.__checkForErrors__ = function () {
if (this.documentElement.tagName == "parsererror") {
var reError = />([\s\S]*?)Location:([\s\S]*?)Line Number (\d+), Column (\d+):<sourcetext>([\s\S]*?)(?:\-*\^)/;
            reError.test(this.xml);
this.parseError.errorCode = -999999;
this.parseError.reason = RegExp.$1;
this.parseError.url = RegExp.$2;
this.parseError.line = parseInt(RegExp.$3);
this.parseError.linepos = parseInt(RegExp.$4);
this.parseError.srcText = RegExp.$5;
        }
    };
//定义Mozilla的loadXML方法  
    Document.prototype.loadXML = function (sXml) {
this.__initError__();
this.__changeReadyState__(1);
var oParser = new DOMParser();
var oXmlDom = oParser.parseFromString(sXml, "text/xml");
while (this.firstChild) {
this.removeChild(this.firstChild);
        }
for (var i=0; i < oXmlDom.childNodes.length; i++) {
var oNewNode = this.importNode(oXmlDom.childNodes[i], true);
this.appendChild(oNewNode);
        }
//载入后检查错误
this.__checkForErrors__();
//没有问题，设置readyState属性为4
this.__changeReadyState__(4);
    };
    Document.prototype.__load__ = Document.prototype.load;
    Document.prototype.load = function (sURL) {
this.__initError__();
this.__changeReadyState__(1);
this.__load__(sURL);
    };
    Node.prototype.__defineGetter__("xml", function () {
var oSerializer = new XMLSerializer();
return oSerializer.serializeToString(this, "text/xml");
    });
}