Horrifying idea: recursively enumerable expressions (REEx)

"This CAN parse HTML, but you'll wish it hadn't."

@Elizafox
relatedtly, since computers in the real world are DFAs and not turing machines and are capable of parsing html [citation needed] it is possible to write a regex representing the states that an html parser goes through on a computer

@charlotte the regex would have to be larger than the maximum representable size of the HTML document by a huge margin is the problem