Accessibility

The WCAG-anchored layer: baseline usability for people using assistive technologies or with perceptual / motor / cognitive differences.

In scope. WCAG 2.2 success criteria across the four POUR principles (perceivable, operable, understandable, robust), ARIA role / state / property correctness, keyboard navigation and focus management, screen-reader support, color contrast, captions / transcripts / alt text, semantic HTML, reduced-motion preferences, cognitive-accessibility patterns.

Not in scope. Ergonomic polish above the WCAG baseline — that's user-experience. Copy clarity unrelated to assistive tech — that's content-integrity. Section 508 as a regulatory-framework obligation (as opposed to the underlying mechanism) — that carries regulatory-conformance as a secondary taxon.

Distinct because. Accessibility is a baseline standards-measured requirement — patterns pass or fail against WCAG criteria. user-experience is the optimization surface above that baseline. A pattern about "modal lacks focus trap" is accessibility (violates WCAG 2.4.3); a pattern about "modal animation is jarring" is user-experience.

Conceptual sub-structure. Perceivable, operable, understandable, robust — mirroring WCAG POUR.