How do I delete or unregister a registered custom item?

I am currently testing the performance of custom items, so I stumbled upon the need to unregister a previously registered item. There was nothing I could do about it.

I think it probably might be needed, but before I go into more detail on this issue, I will not make any assumptions.

I know I can do this with a page refresh, but that's not the point.

What I have done so far to register the element native, spec-like way:

document.registerElement('my-element', {
    prototype: Object.create(HTMLElement.prototype)
});