The HTML Elements Time Forgot

It is a hard element to get much info about, and it seems I'm not alone in thinking that, as the very interesting and well-worth-a-read document Working NEXTID Tag Element Example has this to say: It is also probably one of the least understood of all of the early HTML elements, being poorly documented, not explained in any depth anywhere, and those who obviously understood how it worked couldn't be bothered to explain it to the rest of us. It is easy for us to look back from the year of our lord ${new Date().getFullYear()} and ridicule what obviously wasn't to be, but these stumblings have made HTML what it is today.