Error · landmark-complementary-is-top-level
Sidebar nested inside another area
Lighthouse / axe call it: Aside should not be contained in another landmark
A sidebar is inside the main content, so it is announced in the wrong place.
Who it leaves out: blind people (screen readers)
How to fix it
Move it outside. Developer task.
In the code
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Related errors
Automated testing covers roughly half of WCAG criteria; a full conformance claim also requires manual review. Technical information, not legal advice.