In plain language
The focused element must never be completely hidden behind sticky bars, banners, or popups.
Who it affects
Sighted keyboard users when sticky chrome would otherwise hide the focused control.
How to check
Tab through pages with sticky headers/footers/banners open: the focused element must remain at least partly visible at all times. Worked example — An online clothing store's product listing page: open a non-modal dialog/popover over page content, then Tab: if the background content remains focusable and gets fully hidden underneath, it fails.
Common misconception
Teams confuse this with 2.4.7 (focus visible). This rule is about whether a sticky header or banner physically covers the focused element, even if the focus outline itself is perfectly visible. Real example: on a government tax-filing portal, a sticky header/footer completely covers the element that currently has keyboard focus — the user is 'somewhere' they cannot see.