var dom = {
	'add_event_listener' : function (evnt, elem, func) {
		if (elem.addEventListener)  // W3C DOM
			elem.addEventListener(evnt,func,false);
		else if (elem.attachEvent) { // IE DOM
			var r = elem.attachEvent("on"+evnt, func);
			return r;
		}
		return false;
	}
	, 'addClass' : function (elem, class_to_add){
		elem.className += ' '+class_to_add;
	}
	, 'delClass' : function (elem, class_to_del){
		var arr = elem.className.split(' ');
		for (var i = arr.length -1; i >= 0; i--){
			if ((arr[i] == '') || (arr[i] == class_to_del)){
				arr.splice(i,1);
			}
		}
		elem.className = arr.join(' ');
	}
}