My introduction to roff and co. as a typesetting system was the 1997 edition of Dale Dougherty and Arnold Robbins's Sed & Awk. Many of the book's examples are geared toward automatically inserting/correcting roff macros. I can't recall a specific example from the book, but it would be something like "insert the roff 'section' macro on matches of `/^CHAPTER/`."

Ultimately, it's probably not practical, but I liked the idea of using UNIX utilities to get around worrying about markup altogether during the writing process. The book isn't really about roff, so I only got a sideways view of this kind of workflow. Was this "a thing" in the 90s?