I really liked Mastering Regular Expressions by Jeffrey Friedl. He goes in depth on what they are (with a bit of FSA background) and how a regex engine works. It helps conceptualize what's going on and how to know what your specific regex library is doing. Does that matter all that much? Not necessarily, but it's good to know things like whether or not your regex can blow in time complexity due to back tracking or... - Source: Hacker News / 5 days ago

The only good thing to come out of regular expressions is https://regexcrossword.com/. - Source: Hacker News / 5 months ago

I thought this crossword, where one can start learning regex step-by-step. A great app, though. https://regexcrossword.com/. - Source: Hacker News / 8 months ago

I love the less maniacal version of this https://regexcrossword.com/. Really useful for anyone who wants to get a little better at regex without hating themselves. Source: about 1 year ago

I used to have to look up regexes every time I needed to use them, but I was able to learn them pretty quickly with O'Reilly's Mastering Regular Expressions. Highly recommend that book plus https://regexcrossword.com/ for practice interpreting other people's expressions. Source: about 1 year ago

If I got your point correctly, I think markdown is a great solution for this. For this particular app, I used react-markdown as parser but there are other libraries of course. Source: about 3 years ago