English Phrase: By the book
Yes, this is yet another phrase related to books. By the book means to follow the laws or rules exactly as they are written in the law record books.
Some people are very strict about correctly following the rules. With this type of person, there is no leeway or wiggle room.
Now, this may sound a little bit severe or harsh, but in some cases, it is imperative to go by the book or follow the rules very carefully.
Think about immigration officers, police officers, doctors or bridge construction companies, for a second.
If they try to bend the rules, even just a little bit some horrible things could happen.
People could die, for instance.
Sometimes it’s necessary to follow the rules or laws very carefully, and in these cases, you must go by the book.