My A-ha! moment

So I'm working some freelance webdesigns and I can't believe, in nearly 12 to 13 years worth of doing this, I never figured this out -- have two index.html pages, one labeled index and the other index2, and work off the index2, and use that as the browser preview/experimental pages. See, in the past I've always just worked off the index page and then I'd find something nutty, would change it, save it in order to preview, and then realize, dang it, I can't undo. By doing it this way, I was actually able to preview, see if I liked it, and then if it worked, save it over the other index file, without losing hours worth of work.

I'm sure this has been obvious to everyone for years, but man...