All page content must be contained by landmarks
How to Fix the Problem
Ensure all content is contained within a landmark region, designated with HTML5 landmark elements and/or ARIA landmark regions.
Screen reader users can navigate to a section based on its HTML element or ARIA Landmark. For example, you might use ARIA Landmarks to provide a simple replacement for a skip navigation link, though the replacement is only useful for users of screen readers. Sighted users or people using screen enlargers won't benefit from the addition, so it's not a good practice to substitute ARIA landmarks for skip navigation links altogether.
The markup in the following example shows native HTML5 landmark elements:
<html lang="en"> <head> <title>Hello</title> </head> <body> <header>This is the header</header> <nav>This is the nav</nav> <main>This is the main</main> <footer>This is the footer</footer> </body> </html>
ARIA best practices call for the use of native HTML5 landmark elements instead of ARIA roles where possible, but the markup in the following example works:
<html lang="en"> <head> <title>Hello</title> </head> <body> <div role="banner">This is the header</div> <div role="navigation">This is the nav</div> <div role="main">This is the main</div> <div role="contentinfo">This is the footer</div> </body> </html>
Why this is Important
Navigating a web page is far simpler for screen reader users if the content splits between multiple high-level sections. Content outside of sections is difficult to find, and the content's purpose may be unclear.
Historically, HTML lacked some key semantic markers such as the ability to designate sections of the page as the header, navigation, main content, and footer. Using both HTML5 elements and ARIA landmarks in the same element is considered a best practice, but the future favors using native HTML5 element regions as browser support increases.
It is best practice to contain all content excepting skip links, within distinct regions such as the header, nav, main, and footer.
The Algorithm (in simple terms)
Ensures that all content on a page is contained within a landmark region.