function foo() {
	var doc = document.evaluate("//td[@class='b']", document, null, XPathResult.ANY_TYPE,null);
	var iter = doc.iterateNext();
	var i = 0;

	while (iter) {
		if ((i % 2) == 1) {
			iter.innerHTML += "<br>test<br>";
		}
		iter = doc.iterateNext();
		i++;
	}

}

foo();