It is absolutely amazing how many things we can do with CSS. It's as powerful as some programming language, while in fact being completely declarative and super fast at the same time!
I understand a proper parser would (perhaps) be more complex, but could also be open sourced in a lower level lang such as C, and then used by everyone, there's also already the full test suites for testing the output - maybe even Google+MS+Moz could open a contest - "fastest, most readable and efficient parser in C (or rust, wtv) takes 10k home"