Event.observe(window, 'load', startup, false);

function startup() {
	var hoverables = document.getElementsByClassName("hoverable");
	hoverables.each(function(e) {
		var children = e.getElementsByTagName("tr");
		for(i = 0; i < children.length; i++) {
			child = children[i];
			Event.observe(child, "mouseover", handleMouseOver, false);
			Event.observe(child, "mouseout", handleMouseOut, false);
		}
	});
}

function handleMouseOver(event) {
	var e = Event.element(event).parentNode;
	e.addClassName("hover");
}

function handleMouseOut(event) {
	var e = Event.element(event).parentNode;
	e.removeClassName("hover");
}