it just explains like “this is what happens when you run the code” instead of “here is how the code works”, if you want to know the latter please read <a href="https://www.oilshell.org/archive/Thompson-1968.pdf" rel="nofollow noreferrer">https://www.oilshell.org/archive/Thompson-1968.pdf</a><p>Regex is something of an early JIT compiler