landmark-no-duplicate-banner
Page must not have more than one banner landmark
manualconfidence: mediumseverity: minoroperable
Checks that at most one banner landmark (role="banner" or a non-nested <header>) exists on the page.
Applies to. Applies whenever the page contains at least one banner landmark (explicit role="banner", or an implicit, non-nested <header>; see landmark-banner-is-top-level's implementation notes for the shared landmark-detection model).
Expectation. At most one banner landmark exists on the page. Per WAI-ARIA Authoring Practices, the banner landmark represents site-oriented content that identifies the page as a whole, so having more than one is ambiguous for assistive technology users navigating by landmark.
Examples
can't tell
<body><header>First</header><header>Second</header></body>
Two top-level `<header>` elements both resolve to the banner role.
n/a
<body><header>Site header</header></body>
Only one banner landmark exists.