Web pages differ from books and other documents in one crucial respect: hypertext links allow users to experience a single web page separate from its context. For this reason web pages need to be more independent than pages in a book. For example, the headers and footers of web pages should be more informative and elaborate than those on printed pages. It would be absurd to repeat the copyright information, author, and date of a book at the bottom of every printed page, but individual web pages often need to provide such information because a single web page may be the only part of a site that some users will see. This problem of making documents freestanding is not unique to web pages. Journals, magazines, and most newspapers repeat the date, volume number, and issue number at the top or bottom of each printed page because they know that readers often rip out articles or photocopy pages and will need that information to be able to trace the source of the material.