renderPriority and iframes

[antosart]

I was wondering whether the new renderPriority attribute will have effects on iframes (either because it is set on the iframe element itself or because it is inherited from an ancestor element). If so, could this have security/privacy implications? By assigning different renderPriority to different iframes, you could get rendering timing information about a (possibly cross-origin) iframe.

[vmpstr]

I think this is a fair point. My initial thoughts is that we would either allow rendering to happen in iframes or we wouldn't. I don't think we would be able to enforce something like background priority for iframes (especially cross origin)

[antosart]

Ok. I think it would be good to spell out in the explainer how iframes would behave w.r.t. this attribute.

[chrishtr]

I think we should definitely let renderPriority affect iframes, since some content needs to be put in iframes and it's still a legitimate use case to pre-render iframe content.

That being said, we should work carefully through appropriate mitigations for priviacy and security as necessary.