We may be talking about different things. Parsing valid, standard-conforming HTML/Markdown/whatever is a solved problem. Getting multiple parsers to deal with a

We may be talking about different things. Parsing valid, standard-conforming HTML/Markdown/whatever is a solved problem. Getting multiple parsers to deal with arbitrary tag soup, authoring errors, variously-supported extensions etc in a consistent way is a lot uglier. The problems may be commercial/political/educational/organizational rather than technical, but that doesn't mean they aren't real.