It's the Search tab at the bottom. The problem is it's optimized for search more than replace. I don't know that I have to press Search first to have it update the occurrences list before I can replace it. I think it's like other text editors. I simply type the new search string and the new replace string (the previous time I didn't do the replacement). It used the previous search string and replaced using my newly entered replace string. And it seems it commits directly to the disk, so there is no way to undo the damage. Luckily, I have git, otherwise I have corrupted the whole code base I'm working on.