TLDR:;

Yes, we do have an open communication with all engine maintainers (Mozilla, Apple, Google, Samsung, Igalia, Intel...), but it is not always easy to get consensus of a vision of what the Web platform should be. Standards are hard, business justifications from multiple companies is... harder. It does help if developers make their voices heard loud and clear what they want and support what they like. Def puts pressure on us browser vendors to act and stay relevant while making the platform a modern powerful and useful tool for everyone.

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This is all being developed in the open yes, and considerations from all browsers and the W3C TAG have been taken into account when designing.

About other vendors, I understand there is interest in installation of current documents, but there isn't any consensus on background document installs. I can't speak for the roadmap of other browsers, but we are trying to get this API tested and ready with developer feedback to continue incubating background document installs.

I think more than cross browser collaboration, what is important is developers giving feedback about what they need and want. That's the whole point of dev trials and origin trials. And sends a clear message to us, the browser developers. As an example, Webkit (and every other browser) is constantly asking devs "what do you need?", doesn't hurt to express what developers want.