Focus Not Obscured (Minimum)
When a user interface component receives keyboard focus, the component is not entirely hidden due to author-created content.
In plain language
If someone navigates your software using only the keyboard, the focused element must never be completely hidden behind another element on screen.
Why it matters
People who can't use a mouse rely on the keyboard to navigate. If the focus lands behind a sticky header or chat widget, the user is lost and can't use the product.
In practice
Fails this criterion
A user presses Tab and focus moves to a button, but a sticky header covers that button entirely.
Meets this criterion
Sticky headers, cookie banners, chat widgets and modals never completely cover the focused element.
Test it yourself
Press Tab through the entire interface. If any fixed element on screen — a header, banner, or chat widget — completely covers the focused item, this criterion is failing.