[avidal]

I personally use XXX all the time; but I tend to use it in places where perhaps ATTN or NOTE would be more explicit.

It may be simply an artifact of other code in the past; when I switched to vim ~10 years ago I noticed XXX was specifically highlighted along with FIXME and TODO and so I used it as a third option: here's something that doesn't need to be fixed, isn't really a todo, but you should read and understand.

Interestingly, I just did a quick check in vim to see which prefixes were highlighted and ATTN / HACK were not, but the usual suspects (BUG, FIXME, TODO, NOTE, XXX) were. I should probably use NOTE in most places that I currently use XXX...