Rule: complementary landmark: must be top level

• complementary landmarks provide a way to identify sections of a page that may not be considered the main content, but that provide important supporting or related information to the main content.
• Top-level landmarks are the easiest to find and navigate to using assistive technologies.

Success Criterion 1.3.1 Info and Relationships

Other Related Success Criterion:

• Success Criterion 2.4.1 Bypass Blocks
• Success Criterion 2.4.6 Headings and Labels
• Success Criterion 2.4.10 Section Headings

• Use an aside element to define a complementary landmark.
• If the aside element technique is not being used, a role="complementary" attribute on the container element of the supporting content can be used to define a complementary landmark.
• When creating the landmark structure on the page, ensure that the complementary landmark is a top-level landmark (i.e., it is not contained within any other landmarks).

• Accessible Rich Internet Applications (WAI-ARIA) 1.2 Specification: complementary role
• HTML5: The ASIDE element
• WAI-ARIA Authoring Practices 1.2: Landmarks
• WAI-ARIA Authoring Practices 1.2: Landmark Example
• W3C Web Accessibility Tutorials: Page Structure
• ARIA11: Using ARIA landmarks to identify regions of a page
• ARIA13: Using aria-labelledby to name regions and landmarks
• ARIA14: Using aria-label to provide an invisible label where a visible label cannot be used