That's where he lost me as well, I've written a few parsers and seen a lot of compiler implementations, and almost never is a regex library a part of the equation.

Regexes aren't powerful enough for a full language, so you'll have to write your own lexer/parser anyway (or use a parser generator). And once you're going down that road, it's pretty awkward and unnecessary to try to jam in a regex library to only parse subsections.