//var xml holds the Document Object
var priceElements = xml.getElementsByTagName("price");
//returns a NodeList of all elements with the tag price 
var i;
for (i=0;i < priceElements.length;i++) { // looping over all those price elements
     var USAprice = parseFloat(priceElements.item(i).firstChild.nodeValue);
     //the firstChild property returns the Text node
     //of this Text node we take the nodeValue, being the text itself
     //we convert this text to a number (floating)
     priceElements.item(i).setAttribute("unit","Canadian dollar");
     //we set the attribute "unit" to value "Canadian dollar"
     var convertedprice = USAprice * 1.4;
     //we convert the price to Canadian dollar
     var newprice = xml.createTextNode(convertedprice);
     //we create a new Text node containing the new price
     priceElements.item(i).replaceChild(newprice, [ccc] priceElements.item(i).firstChild);
     //we replace the old Text node with the new one
     }