IMHO it didn't mean anything, just like when you're logging to console a lot and you want to quickly mark/separate something quickly, you're maybe adding bunch

IMHO it didn't mean anything, just like when you're logging to console a lot and you want to quickly mark/separate something quickly, you're maybe adding bunch of '======', similarly XXX is just a quick mark to go back - so it's easy to find it - and sort something out there. I think it was used more in days when we didn't have meta-comments - comments that ide is smart about now (FIXME is highlighted, indexed etc). Novadays I'd use it in the code that really needs to be fixed because it smells. I wouldn't get offended when team member would say - don't use XXX, use FIXME or TODO only - because XXX'es shouldn't leak to commits anyway. That's my opinion/gut feeling.