While responseText returns the HTTP response as a string, responseXML returns the response as XML
" responseText”属性以字符串形式返回HTTP响应；“ responseXML”属性以XML形式返回HTTP响应。

The ResponseXML property returns an XML document object, which can be examined and parsed using W3C DOM node tree methods and properties.
“responseXML”属性返回了一份XML文档对象，可以使用W3C DOM节点树方法和属性对该XML文档对象进行检查和解析。