Basic text stuff. I would find this REALLY useful especially when you have to be very stringent about code formatting and having to search for multiple spaces vs tabs in a 6000+ line document can be come quite tedious. In fact, I have to use separate app.
Having a menu option to see white space characters would make this much simpler and I wouldn't have to switch apps.
Show paragraph characters (that funky looking P) and use something like >> (raquo) for a tab character and middots for spaces, would be my suggestion.
Thanks!