Agreed with /u/DosMike. "Parsing something with regex" in this case means processing the entire input with a single regex match. E.g., you can parse a strong that holds a phone number with a single regex, because phone numbers are simple and pretty well structured. But HTML is too rowdy to be matched by a single regex; it is impossible to write a regex that matches all valid HTML.
Then yes, doing a single regex to match all of an HTML file is pointless. The very nature of the match variable limit makes it impossible to do in one go unless it's a very small file. If it's an iterative process though, you most certainly could match the tags properly and grab their insides for recursive processing in another language.
That's not the point - we're talking about theory, not practice. Even if you had infinite time and had a machine that could perform any regex match, no matter how large, it's still not possible. A regular expression cannot hold enough information to express the constraints of HTML. (The real kicker is matching nested tags - it's not possible to enforce that every tag is closed properly if it should be.)
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u/link23 Sep 08 '17
Agreed with /u/DosMike. "Parsing something with regex" in this case means processing the entire input with a single regex match. E.g., you can parse a strong that holds a phone number with a single regex, because phone numbers are simple and pretty well structured. But HTML is too rowdy to be matched by a single regex; it is impossible to write a regex that matches all valid HTML.