HTML / XML / JS, low-level validity (cross-cutting)MediumVerified
Duplicate id attributes
What it is
Repeated ids.
Why it matters
Breaks in-page anchors and ARIA references (a11y/agents).
How to fix it
Make ids unique.
Impact
Low-medium; a11y/agents. Direct (WCAG/ARIA parsing).
Evidence
Unique ids are required for valid ARIA/anchors. W3C, Web Content Accessibility Guidelines (WCAG) 2.2; W3C, WAI-ARIA Authoring Practices