nav ul.menu {
	display:inline-block;

	li {
		display:inline-block; // or use float:left;
		list-style:none;
	}

	> li { // first children of ul.menu (primary menu)

		ul {
			display:inline-block;
			opacity:0;
			@include single-transition(all, 500ms, ease-in-out);

			li { // secondary menu

			}
		}

	}

	> li:hover {

		ul {
			opacity:1;
			@include single-transition(all, 500ms, ease-in-out, 500ms); // delay fade out
		}
	}
}