I think he means the "supplemental material" CDs that many textbooks come with these days, which are just a fancy way of forcing the user to use the website, wh

I think he means the "supplemental material" CDs that many textbooks come with these days, which are just a fancy way of forcing the user to use the website, which of course requires a subscription fee and the surrender of personal information in order to use, and whose use is required by the class and therefore by the university.