Regular expressions match regular languages (hence the name). If your language involves pairs of things (e.g HTML), it's not regular. Perl hacked support for this in via backreferences and other extensions, but these are slow and illegible. Use a proper context-free grammar parser if you need to parse a context free grammar, you know?
More broadly, people fear and misunderstand regexes because they have no idea how they work. It becomes much easier if you understand how they map to deterministic finite state machines. Recommended reading: https://swtch.com/~rsc/regexp/regexp1.html
Once you understand how they work, you can basically read a regex left to right and intuitively know all the strings they'd match. There is no such thing as an unmaintainable/illegible basic regex - they're just words with some placeholders in them - it's when you cram in extended functionality (which is basically a programming language where all the keywords are single characters) that shit hits the fan.
More broadly, people fear and misunderstand regexes because they have no idea how they work. It becomes much easier if you understand how they map to deterministic finite state machines. Recommended reading: https://swtch.com/~rsc/regexp/regexp1.html
Once you understand how they work, you can basically read a regex left to right and intuitively know all the strings they'd match. There is no such thing as an unmaintainable/illegible basic regex - they're just words with some placeholders in them - it's when you cram in extended functionality (which is basically a programming language where all the keywords are single characters) that shit hits the fan.