I was there like fifteen - twenty years ago before the hyphen standard and shadow dom and all that when JS libraries briefly leaned into just making up their own elements. I think everyone collectively agreed that it was a bad idea and it fell out of popularity.

If I were going to use them, I'd be inclined to vendor them just to prevent any sort of collision proactively

    <donatj-fancy-element>
        <donatj-input />
    </donatj-fancy-element>