One thing not mentioned here which I think is good to be aware of as you write intermediate to advanced regexes is understanding "catastrophic backtracking" and

One thing not mentioned here which I think is good to be aware of as you write intermediate to advanced regexes is understanding "catastrophic backtracking" and how to mitigate it: https://www.regular-expressions.info/catastrophic.html https://www.regular-expressions.info/catastrophic.html For some reason I enjoy figuring regexes out. What I usually do is TDD them, I have a mini test suite of examples of strings I want to match and strings I don't want to match and I write some code to apply a candidate regex to them all and validate, and then I iterate until it passes. Then I rewrite the regex in extended regex format and add comments so that other people or future me understand what's going on. Doing what a good regex can do with regular code instead (which you might do with the goal of readability or maintainability) is usually much much MUCH slower, FYI