HTML Processing Model: Event Loop step is wrong

[smfr]

The proposed "HTML Processing Model: Event Loop" step is incomplete:

For each fully active Document in docs, Run the update intersection observations steps for each IntersectionObserver whose root is in the DOMtree of that Document.

This doesn't catch scrolling a frame having a subframe with a targeted element, i.e observers in subframes with an implicit root need to run when any ancestor frame gets scrolled or laid out.

[szager-chromium]

The implicit root is, by definition, in the DOMtree of the top-level document.

But leaving that aside, I'm wondering why this would be an issue. If the HTML event loop is running, then every active document will run these steps. Does it matter whether the IO steps run when the the top-level document is processed, or when the embedded document is processed?

[miketaylr]

@smfr any thoughts? Or should we close this issue?