var mainRules = {
	'a.menu': function(element){
		var cache = new Image()
		var img = element.firstChild
		cache.src = img.over || img.getAttribute('over')
		element.onmouseover = function() {
			var img = this.firstChild
			img.src = img.over || img.getAttribute('over')
		}
		element.onmouseout = function() {
			var img = this.firstChild
			img.src = img.out || img.getAttribute('out')
		}
	}
}
Behaviour.register(mainRules);