## 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.

## 2025-05-24 - Skip Link Focus Management
**Learning:** For a "Skip to content" link to effectively move focus in an SPA, the target container (e.g., `<main>`) must be programmatically focusable. Simply having an ID is not enough; `tabIndex={-1}` is required. Additionally, standard browser behavior might show a focus ring on the container, which is often undesirable for non-interactive wrappers, so `outline: 'none'` should be applied inline or via CSS.
**Action:** Always add `tabIndex={-1}` and `outline: 'none'` to the target of a Skip Link (`#main-content`) to ensure correct focus behavior without visual clutter.