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WCAG: Best Practice: Main landmark must not be contained in another landmark
It is a best practice to ensure the main landmark is not contained within another landmark. All content should be contained within distinct regions such as the header (
role="banner"), content (
role="main"), and footer (
Navigating a web page is far simpler for screen reader users if the content splits between some high-level sections. Content outside of these sections is difficult to find, and its purpose may be unclear.
HTML has historically 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 probably favors HTML regions as browser support increases.
The HTML Living Standard states "A hierarchically correct main element is one whose ancestor elements are limited to <html>, <body>, <div>, <form without an accessible name, and autonomous custom elements. Each main element must be a hierarchically correct main element." This may reflect a "best practice" based on W3C validation.