function doZebra () {
	var tables = document.getElementsByTagName("tbody");
	for (var i = 0; i < tables.length; i++) {
		if (tables[i].className == 'zebra') {
			zebra(tables[i]);
		}
	}
}

function zebra (table) {
	var current = "odd";
	var trs = table.getElementsByTagName("tr");
	for (var i = 0; i < trs.length; i++) {
		trs[i].className = current;
		current = current == "even" ? "odd" : "even";
	}
}
window.onload = doZebra;