Re: [w3ctag/design-reviews] Declarative Shadow DOM (#494)

> Looking at this with @hober, I was trying to understand what was the major fear that people have with not supporting streaming. It seems to be that there is fear that web sites that are 100% bought into web components in the sense that even their app root element is a custom element, might loose incremental rendering.

Thanks for the comment! Developers want streaming (e.g. [comment](https://github.com/whatwg/dom/issues/831#issuecomment-633030551)), to improve FCP and similar metrics. As you mentioned, the extreme case of that is a `<my-app>{everything else}</my-app>` type site, where nothing will be rendered until the closing `</my-app>` tag is parsed. But even absent that, for large individual components, there might still be an FCP hit if streaming is not supported.

Having said that, I think the streaming ship has sailed, as there is [strong pushback by WebKit](https://github.com/whatwg/dom/issues/831#issuecomment-671545842) on streaming support. And Gecko has been mostly quiet about the feature, except to say they [wouldn't support a "streaming-optional" implementation](https://github.com/whatwg/dom/issues/831#issuecomment-650107249). So in order to gain 2-implementer support, I'm punting the streaming feature.

> As I understand you already have an experimental implementation, so I am wondering if that is really the case? I also believe it would be great to have this discussion as part of the explainer.

Chromium does have an experimental implementation, but we don't have data on this aspect yet. It might be difficult to gather such data, as the feature doesn't support streaming. There is a brief discussion of this aspect of the design in the explainer, [here](https://github.com/mfreed7/declarative-shadow-dom/blob/master/README.md#timing-attach-the-shadow-on-opening-or-closing-template-tag).

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