Nested html elements

Hi,

I wonder if it's possible with web-types to require a certain hierarchy between HTML elements.

A bar example:

```html

```

As with standard `li`, `my-li` make no sense out of the `my-ul`context.

Also, I have this other issue with so called `HTML Web components` where my component is only used to enhance and wrap a standard HTML tag. Is there a way to support it?

I've tried to nest the `html` properties under another `elements` but without success. I looked as some example, particularly `Bootstrap-vue` and I couldn't find a relationship between for example `BBreadcrumb` and `BBreadcrumbItem`.