I learned this back when HTML5 was brand new around 15-ish years ago. If you wanted to use the new tags like <article>, the only “polyfill” needed was some css styles. You can see it in the early versions of the HTML5 Boilerplate:

https://github.com/h5bp/html5-boilerplate/blob/v0.9/css/styl...

I realized that I could just make up tags and style them and it was work.