It might be nice to touch on composition as a good way to get started is to test out individual pieces and be confident they work when you're putting them toget

It might be nice to touch on composition as a good way to get started is to test out individual pieces and be confident they work when you're putting them together. If you're building a complex regular expression, setting smaller parts in variables and dropping them in with (?:${part}) makes things a bit more readable. It also exposes a real weakness of most regex engines. In particular, alternation is a first-class operation, but complement and intersection, while theoretically possible[1] are typically not. A person might guess that to match three keywords is /.keyword1.&.keyword2.&.keyword3./ Or maybe /.keyword1.&(.keyword2.)!/ to match keyword1 and not keyword2. But those won't work, so it's a good idea to explain some options, an obvious one being /keyword1/.test() && !/keyword2/.test() In the section on lookaround assertions, it's probably useful to note that (?=thing1)(?=thing2) can match both, and it's a good mental model for it, but that it comes with a few gotchas. [1]: https://www.researchgate.net/publication/220994310_Succinctness_of_the_Complement_and_Intersection_of_Regular_Expressions https://www.researchgate.net/publication/220994310_Succinctn...