Back in the 1980s, before MS Word was the unquestioned king of the desktop, there was a DOS word processing program called WordPerfect. Everyone used it.

WP had a feature where you could press a special key combination and the screen would split. The top would have your text (not WYSIWYG, that was way in the future, although WP could show an approximation).

In the bottom part you could see your text, along with every control ~~coffee~~ code that turned bolding in or off, marked text for a table of content, etc.

Not only could you see it, you could navigate through it and delete codes, or watch the codes change as you edited text in the to half of the screen.

It gave you a control that I still miss these days. No more wondering why your word processor is doing columns wrong, or why the image you inserted doesn't line up properly.

Check it out (starting at around 4:20).