Not having contractions.

[TheLobster]

Most of my professional editing and proofreading is for banks, law firms and the like. When I started to write for fun, that was a habit I had to break. I still sometimes catch myself uncontracting.

Ironic how it’s your pastime fiction writing where you’re having all those tense contractions, but in your day job, your language finally gets to relax and unwind

 

[XerXesXu]

Editors are often much MORE knowledgeable than writers about acceptable conventions, because it's their job to know them.

You've missed the point of his book, which originated as an in-house guide for copy editors.

He was the head copy editor at Random House. His book was guidance for his junior copy editors, who might think the conventions they applied because 'it was their job to know conventions', did not apply in Random House, whose conventions were more permissive.