Notifiy subscribers for changes
function(property, val) {
		if(val === undefined) {
			// if second argument is missing, use property as value
			val = (property === undefined) ? this : property;
			property = "__all__";
		}
		
		if(property == "__all__") {
			// notify global subscribers
			notify(this._subscribers["__all__"], val);
		}
		else {
			// notify all subscribers of property
			notify(this._subscribers[property], val);
			
			// notify global subscribers as well
			this.notify(/*TODO: some usefull value*/);
		}
	}