Pages 70-71 in which the author discusses Secondary, tertiary and whatever comes after tertiary. The most common mistake in web design especially in larger sites is failing to give a lower-level navigation the same attention as the top. After the second level usually the navigation breaks down and becomes ad hoc.
This happens because is hard to design given the limited amount of space on the page and the number of elements that have to be squeezed in. Is really important to pay attention to the other levels, because as indicated in the reading users usually end up spending as much time on lower level pages as they do at the top. The vital point is to have sample pages that show the navigation for all the potential levels of the site before you start thinking about colors and other secondary design decisions.