Export dfns for Page Visibility spec

[marcoscaceres]

Non-normative changes... just exports.

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/browsing-the-web.html ( diff )
/history.html ( diff )

[domenic]

I'm not sure what to do here, as the usages of these terms are by a spec which pretty clearly monkey-patches HTML in bad ways. For example, the usage of "session history entry" is in an algorithm that reads "When the user agent determines that the visibility of the Document of the top-level browsing context has changed ... If traversing to a session history entry ...". The correct thing to do here is to actually update HTML's session history traversal algorithm, so that implementers working on that algorithm can see how it works.

That is to say, if the specifications were properly layered, "session history entry" would not be a concept that is referred to by specs outside of HTML. So I don't think we should export it, and encourage further abuse of this sort.

The other two "change steps" though are definitely meant to be exported, so that portion of the patch makes sense. Although I note that "session history document visibility change steps" isn't actually used by the Page Visibility spec, and the way in which it uses "unloading document visibility change steps" is incorrect. (It doesn't define the steps, it just references them during its monkey-patch algorithm.)

[marcoscaceres]

Can I just say that... I love this! This is exactly the kinds of bugs that I'm hoping we will find as we move folks to be entirely dependent on exported definitions from cross references (I know, I'm preaching to the choir - but still, it's exciting!).

I'm not actually involved with the Page Visibility spec, was just doing some cleanup... so will take the above back to the Web Perf WG and file a bug there.

[domenic]

Let's close this until such a time as Page Visibility is properly layered on to HTML.