Xiaocheng: Discussed it at B, as we didn’t have enough agenda items. Already posted a reply. Nothing to discuss today.

Xiaocheng: Early design review and it proposes a new type of action for speculation (adding to prefetch and prerender). This does prerender, but doesn't run any script. Parsing HTML pauses if there is blocking script. ...middle ground seems good. Like to see some study on the use of script and what the effect of this would be.

Martin: Why can't prefetch do this?

Xiaocheng: prefetch doesn't fetch sub-resources and doesn't parse.

Martin: Parsing doesn't have observable effects, it's just the subresources that matter.

Xiaocheng: Chances are that finding subresources will hit script execution.

Martin: Two things: stuff you might need as data (prefetch) and stuff that you might navigate to (prefetch or prerender). Prerender needs extra information about where content might appear, but then you have subresource fetching (side effect) and script execution (another side effect).

marcos: Prerender creates a new context.

Xiaocheng: It does everything, short of show the content.

Martin: Is it only top-level navigation?

Xiaocheng: How about we suggest that they test for efficacy (http archive?). Also think about strategies. Preparsing only? (Which would have to block on script execution.)

Marcos: prerender is only for top-level navigations.

Martin: preparse would work for an iframe, wouldn't it? (not sure)

Marcos: It does annoy me that it is for the react use case, catering to something sites that use weird tools. It seems like it is solving the problem. A lot of people use React and this helps, but the other side is maybe you should put content in your page and not depend on script to populate it.

Martin: Is the implication that these scripts have unwanted side effects?

Marcos: Not my reading. Not sure what is going on with <iframe src=javascript...

Xiaocheng: Target case is for pages that can be mostly rendered statically, they don't want to load ads until the page is shown. Question remains: how useful is this? How often can it be used?

Martin: Ads case seems real. But don't ads run intersection observer? Maybe they just want to keep load down.

Xiaocheng: they should evaluate the success rate of the strategy.

Martin: They should also look at alternatives, like just preparse as a step toward this. So how much does the subresource loading get you? Or, could you limit the subresource types? That might need some controls rather than a single mode. For example, ads might use script exclusively, so no script execution is fine. But others use pixels for tracking and so loading images could be bad.