[nomel]

These sorts of questions are what I call “Easter eggs”. If someone understands the actual complexity of the question being asked, they’ll be able to give a good answer. If not, they’ll be able to give the naive answer. Either way, it’s an Easter egg, and not useful on its own since the rest of the interview will be representative. The thing they are useful for is amplifying the justification. You can say “they demonstrated a deeper understanding of Unicode by pointing out that a naive approach could be incorrect”.

[ethbr1]

E.g. Can you completely parse HTML with regex?

[Cthulhu_]

You can't parse [X]HTML with regex. Because HTML can't be parsed by regex. Regex is not a tool that can be used to correctly parse HTML. As I have answered in HTML-and-regex questions here so many times before, the use of regex will not allow you to consume HTML. Regular expressions are a tool that is insufficiently sophisticated to understand the constructs employed by HTML.

etc. https://stackoverflow.com/a/1732454

[astrange]

If by "parse" you mean "match", the answer is yes because you can express a context-free language in PCRE.

If you mean "parse" then it's probably annoying, as all parser generators are, because they're bad at error messages when something has invalid syntax.

[nomel]

Is this true, in practice, given the lenient parsing requirements of the real world?

[joquarky]

Technically, no

Practically, yes