XML DOM specified Property

var xhttp = new XMLHttpRequest();
xhttp.onreadystatechange = function() {
   if (this.readyState == 4 && this.status == 200) {
       myFunction(this);
   }
};
xhttp.open("GET", "books.xml", true);
xhttp.send();

function myFunction(xml) {
    var x, i, xmlDoc, txt;
    xmlDoc = xml.responseXML;
    txt = ""
    x = xmlDoc.getElementsByTagName('book');
    for (i = 0; i < x.length; i++) {
        txt += x.item(i).attributes[0].specified + "<br>";
    }
    document.getElementById("demo").innerHTML = txt;
}