Comment by jug

Web standards are so powerful today with all the browser native form components etc, so I think one should just exploit that one and use XSLT (https://caniuse.com/?search=xslt) if you want to create an own "UI markup language". It'll render straight to everything that your browser supports, which is a lot. Then just use CSS to style it however you wish if you want to. What's nice about this approach is also that you can create a true domain-specific markup language, which will always be more clean and compact than a generic one.