XML DOM getElementsByTagNameNS() Method

xmlDoc=loadXMLDoc("books.xml");

x=xmlDoc.getElementsByTagName('book');
var newel,newtext;

for (i=0;i<x.length;i++)
{
newel=xmlDoc.createElementNS('p','edition');
newtext=xmlDoc.createTextNode('First');
newel.appendChild(newtext);
x[i].appendChild(newel);
}

//Output all titles and editions
y=xmlDoc.getElementsByTagName("title");
z=xmlDoc.getElementsByTagNameNS("p","edition");

for (i=0;i<y.length;i++)
{
document.write(y[i].childNodes[0].nodeValue);
document.write(" - ");
document.write(z[i].childNodes[0].nodeValue);
document.write(" edition");
document.write("<br />");
}