All of this is part of the semantic web quagmire. To make web pages machine readable. I.e parseable in an unambiguous way. It never caught on because it is triv

All of this is part of the semantic web quagmire. To make web pages machine readable. I.e parseable in an unambiguous way. It never caught on because it is trivial to parse web pages anyway and if you wanted something machine readable, you'd publish your data in json or something. But it's proponents haven't given up yet and are still working on making the web truly semantic.