update Html Render assignment to not put html tag in base class

Folks get a bit confused because we start our the Element base class with an html tag, but later go on to make a "proper" html element.

This is done so they can test the base class by itself. But it would be less confusing to put in a dummy tag, so it's clear it's not the same thing as the HTML element:

maybe "placeholder" or, just "element" -- which isn't are a real html tag.
