Focused elements must not be hidden by sticky headers or overlays

The check takes up to 150 keyboard-reachable elements in document order, iframe included, and skips negative tabindex values and hidden, disabled or zero-size elements. Each gets a plain focus() call, which scrolls the page as keyboard focus does and respects scroll-padding. It runs at every scan viewport, by default 1440 and 390 px wide.

It then tests nine points: the center, the corners and the edge midpoints, up to 3 px inside the edges. Points outside the viewport are skipped. A point is covered when the topmost element there is, or sits inside, a position: fixed or position: sticky container that does not hold the focused element and has an effective opacity of at least 0.1.

When every tested point is covered, the element becomes a finding naming the container that covers most points. A partly covered element goes to needs review, because the check cannot tell whether the visible part still shows what has focus. The scanner does not turn needs review into findings today.