by the book

by the book idiom
Strictly according to the rules, as in Our trip leader is going by the book, allowing us to wander off only for short periods. Shakespeare already used the term figuratively in Romeo and Juliet (1:5): “You kiss by the book.” Also see by the numbers.

The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

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