Finalize how to render to shadowDOM

[phillipskevin]

You currently can render into shadowDOM by setting the viewRoot property:

https://github.com/canjs/can-stache-define-element/blob/75be0f9c937459f6eba13bcf21a09ec7999c26e4/src/mixin-stache-view-test.js#L44

This isn't currently documented because we might want to change how this works. It might be easier to just automatically render into shadowDOM if attachShadow was called and not have a special viewRoot property. Although maybe there will be use-cases for rendering somewhere else, so viewRoot might be useful.

[matthewp]

I think viewRoot is a bit more flexible than checking for a .shadowRoot property. It's explicit and will work with closed shadow roots as well. If a shadow exists then there's probably no point of rendering a template into the light DOM. At least I've never heard of anyone doing that. Keeping viewRoot gives you flexibility here. You could render a template into the shadow (manually) and have the framework render it into the element light DOM. Weird but possible.

[justinbmeyer]

the portal helper is semi-similar ... not sure if this means anything from an API perspective