Hacking lookahead to mimic intersection, subtraction and negation
Note: To understand the following, I expect you to know how regex lookahead works. If you don’t, read about it first and return here after you’re done. I was quite excited to discover this, but to my dismay, Steven Levithan assured me it’s actually well known. However, I felt it’s so useful and underdocumented (the only references to [...]