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There is a tradition in hackerdom of informally tagging important textbooks and standards documents with the dominant colour of their covers or with some other conspicuous feature of the cover. Many of these are described in this dictionary under their own entries. See Aluminum Book, Blue Book, Cinderella Book, Devil Book, Dragon Book, Green Book, Orange Book, Pink-Shirt Book, Purple Book, Red Book, Silver Book, White Book, Wizard Book, Yellow Book, bible, rainbow series.