The knowledge in a physical book is not necessarily a composition, or even a book.

Books can only contain pictures, printed matter or photos, crossword puzzles or paper-cut dolls. In a physical book, a page can be blank, or it can contain a set of abstract lines to support entries, such as in an account book, appointment book, signature book, notebook, diary or sketch book. The pages of some physical books are thick and strong enough to support other physical objects, such as scrapbooks or photo albums. Books can be distributed in electronic form, such as e-books and other formats.