cross-posted from: https://lemmy.sdf.org/post/12950329
Putting a statement into old calligraphy is nice. But it all boils down to because I said so. If you’re going to go to that effort you might as well put the rationale for why it can’t possibly parse the language into the explanation rather than because I said so
The text does technically give the reason on the first page:
It is not a regular language and hence cannot be parsed by regular expressions.
Here, “regular language” is a technical term, and the statement is correct.
The text goes on to discuss Perl regexes, which I think are able to parse at least all languages in LL(*). I’m fairly sure that is sufficient to recognize XML, but am not quite certain about HTML5. The WHATWG standard doesn’t define HTML5 syntax with a grammar, but with a stateful parsing procedure which defies normal placement in the Chomsky hierarchy.
This, of course, is the real reason: even if such a regex is technically possible with some regex engines, creating it is extremely exhausting and each time you look into the spec to understand an edge case you suffer 1D6 SAN damage.
The section about “regular language” is the reason. That’s not being cheeky, that’s a technical term. It immediately dives into some complex set theory stuff but that’s the place to start understanding.
English isn’t a regular language either. So that means you can’t use regex to parse text. But everyone does anyway.
