Interactions between child frames and top-level documents. about explainer-bfcache-ccns

[fergald]

The intention is that this is only useful in the top-level document. I believe on all browsers, the CCNS header only impacts BFCache if it's on the top-level document. CCNS subframes are cached and so it doesn't make sense to me for them to have any influence here (except maybe if they are same-origin as the top-level but then the top-level could just do whatever it is anyway).

Do you have a specific use case or problem in mind?

[antosart]

I don't have a concrete problem in mind at the moment, but I was thinking that in a world after storage (and cookie) partitioning this feature would also need to be partitioned (otherwise it would give a communication channel between A embedded as a cross-site iframe and A as a top-level), so basically it would become useless. So why not restrict the feature to top-level documents from the start?

[Sakda19177]

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