> - never delete any of your valuable code (commenting out is OK)

So how does this work if you want to change a line in a function? Do you just comment out the line and write a new version below it? i.e. if I want to fix a bug in my code, I can't just fix it, I have to add a line of code to my program.

How does this system work in practice? The way I code, it seems like this would lead to a huge file that is mostly commented.