Interaction patterns, form design, onboarding flows, mobile gesture correctness, navigation clarity, notifications, empty states — the behavior layer above the accessibility baseline.
The interaction layer: can the user complete the task the product is designed for?
In scope. Interaction flows (happy-path completion, error recovery in flows), form design (error states, inline validation UX, progress indication, preserving user input on error), onboarding sequences, mobile-specific UX (gesture correctness, viewport, safe areas), navigation clarity, notification UX (timing, dismissal, grouping), empty-state design, task-completion friction, conversion-critical interaction patterns.
Not in scope. WCAG-measured accessibility baseline — that's accessibility. Copy accuracy or truthfulness — content-integrity. Search / AI-crawler visibility — findability. Page-load performance — performance.
Distinct because. The defect is how the page behaves under interaction. The neighboring taxons own baseline-accessibility, copy-truth, index-visibility, and latency respectively. A pattern about "form clears user input on validation error" is user-experience. A pattern about "form missing aria-describedby on error message" is accessibility.
Conceptual sub-structure. Form ergonomics, onboarding / first-run, mobile-platform UX, navigation clarity, notification UX, empty states, conversion flows.