Jonathan

I added type annotations for the rootNode parameter. I also realize now this probably does not correctly handle the special `global` and `host` targets mentioned in the web component example....

I did in fact look into the global target and realized the implementation was a bit off. The correct rootNode is the `contextElement` argument to `swap`. I modified some tests...

I won't implement the host target for this pull request. As far as I can tell, these commits fulfill the objectives of the pull request. However, if it is preferred...