"Checking this page…" is the worker not having answered about the tab yet, which is the same kind of not-finished the publication card already reports with aria-busy. The message carries a `pending` flag and renderStatus marks the status region with it, so "still working" is one question anything outside the popup can ask. Nothing visible changes. It gives assistive technology the region's own state instead of a line it has to re-read, and it gives the capture harness a detection state it can wait for.