## 2024-05-24 - Accessible Input Validation
**Learning:** React 19 renders `aria-invalid={false}` as `aria-invalid="false"`, unlike older versions which might have omitted it. Explicitly handling this in tests is crucial. Also, ensuring DOM cleanup (`cleanup()`) in `afterEach` is vital when testing similar components with same labels across tests to avoid "finding the wrong element" false positives/negatives.
**Action:** Always include `afterEach(() => cleanup())` in `vitest` setup for DOM tests, and expect `aria-invalid="false"` (or explicitly handle `undefined` if omission is desired) when testing valid states in React 19.

## 2024-05-24 - Accessible Loading Buttons
**Learning:** Replacing button text with a spinner destroys the accessible name.
**Action:** Use `aria-busy="true"`, keep children in DOM (visually hidden via opacity/class), and overlay spinner absolutely. Ensure wrapper element replicates flex layout (gap/alignment) to prevent layout shifts.

## 2024-05-24 - Enhancing Inputs Safely
**Learning:** Adding features like character counters to generic input components must handle both controlled and uncontrolled states. Assuming a component is controlled (using `props.value`) can break uncontrolled usage by showing stale data (e.g., sticking at 0/100).
**Action:** When enhancing generic components, detect uncontrolled state (e.g., `props.value === undefined`) and either implement internal state tracking or gracefully degrade (hide the feature) to avoid misleading UX.

## 2025-02-23 - Robust Skip Links
**Learning:** For "Skip to Content" links to work reliably with SPA routers and all browsers, the target element needs `tabIndex={-1}` to be programmatically focusable. Using `transform: translateY(-100%)` for hiding is performant but requires `z-index` management to ensure visibility on focus.
**Action:** Always add `id="main-content"`, `tabIndex={-1}`, and `outline: 'none'` (to prevent focus ring on container) to the target `<main>` element when implementing skip links.