While knowledge how to use regular expression is invaluable, I also recommend learning how they actually work under the hood. It really gives a good lesson when

While knowledge how to use regular expression is invaluable, I also recommend learning how they actually work under the hood. It really gives a good lesson when regular expressions are applicable, and when they're not. From my experience, while many programmers are apt in tools like regexps or grammar->parser generators, they very rarely know how it actually works, which results in people trying to parse HTML with regexps or similar things. It is also a good starting point to some very interesting theoretical stuff like the theory of computations.