alt Hacker NewsRegex has many more features than this, e.g. backreferences. I agree that it's easy to learn enough regex to be dangerous with that subset, but that's not everything regex offers.
Replies
There are hundred different flavors of what "regex" actually means. The basics are often the same but the extended features differ.
The foundation is in theoretical CS with deterministic and nondeterministic finite automata (DFAs and NFAs), and I found it easiest to teach regexes using DFAs since you can then just draw circles and arrows. Regex notation is just a different notation. It's a bit likeif you know piano and then learn another instrument, your brain can always refer back to the piano and it's all much easier.
Backreferences are not really "controversial" but just an extension which does not map to regular languages (those recognized by finite automata). That is, they make regexes "non-regular", so they are more a hack. Regex engines that want to support them need a fundamentally different approach, that's why some don't support them and in principle will never be able to.
Backreferencing inside of a regex (which is a way to find repeat occurrences of a substring) is a very controversial feature that some regex engines intentionally omit, while most others support it only grudgingly. Supporting backreferences opens up a big can of worms: Most regex engines will fall back to a slow, poorly optimised algorithm if they ever encounter backreferences.
Also, it's important for people not to confuse backreferences with capture groups. They look a bit similar, but capture groups are actually fine.
In fact, backreferencing is such a footgun that I don't see it as a possible regex feature. It's a PCRE feature - perhaps even the core distinguishing feature. While all regexes are PCREs, not all PCREs are regexes. It's simply not possible to create a consistently performant implementation of PCRE.