by-the-book
/baɪðəbˈʊk/
/baɪðəbˈʊk/
Etymology
Old EnglishMiddle EnglishModern English phrase
This expression comes from the older phrase by the book, where book meant an accepted set of rules or instructions. It first referred to acting according to written authority, and later developed the stronger idea of following procedures so closely that there is little room for shortcuts or personal judgment.