Adds a listener callback to a DOM element which is fired on a specified event.  Callback is sent the event object and the element that triggered the event
function (elem, eventName, callback) {
		var listener = function (event) {
			event = event || window.event;
			var target = event.target || event.srcElement;
			var block = callback.apply(elem, [event, target]);
			if (block === false) {
				if (!!event.preventDefault) event.preventDefault();
				else {
					event.returnValue = false;
					event.cancelBubble = true;
				}
			}
			return block;
		};
		if (elem.attachEvent) { // IE only.  The "on" is mandatory.
			elem.attachEvent("on" + eventName, listener);
		} else { // Other browsers.
			elem.addEventListener(eventName, listener, false);
		}
		return listener;
	}