Why is checking document validity skipped sometimes?

[mbrodesser-Igalia]

The calls from https://html.spec.whatwg.org/#hide-popover-algorithm to https://html.spec.whatwg.org/#check-popover-validity don't pass the document to https://html.spec.whatwg.org/#check-popover-validity, hence not checking it.

Some, not all, of the calls from https://html.spec.whatwg.org/#show-popover to https://html.spec.whatwg.org/#check-popover-validity check the document.

Might be related to #9367.

[josepharhar]

We only check the document after script has potentially been run and could have moved the element to another document, which happens when we fire events.
Do you think that there are any missing spots which could actually affect the behavior?
Do you think that adding a note would make this better?