Back in 2011, I wasted an entire afternoon on some string handling code that was behaving very strangely (I don’t remember exactly what the code was).

It wasn’t until I loaded the content into a hex editor that I learned about U+00A0, the non-breaking space. Looks like a space, but isn’t.

Ah, yes, the 90s html was jam packed with   (aka  ) to make things not wrap, and that was stellar good fun for copy-pasting

The other "2020s" problem is some leading unicode marks which are also invisible. I thought it was BOM but those do seem to show up to cat but just a few weeks ago I had a file from a vendor's site that wouldn't parse but that both cat and vim said was fine, only to find the wtf? via the almighty xxd