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feat(skills): add frontend accessibility skill (#2048)
Adds the frontend-a11y skill for React and Next.js accessibility patterns. Pre-validated against current main with validate-skills and markdownlint.
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skills/frontend-a11y/SKILL.md
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skills/frontend-a11y/SKILL.md
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---
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name: frontend-a11y
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description: >
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Accessibility patterns for React and Next.js — semantic HTML, ARIA attributes,
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form labeling, keyboard navigation, focus management, and screen reader support.
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Use when building any interactive UI component or form.
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origin: community
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---
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# Frontend Accessibility Patterns
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Practical accessibility patterns for React and Next.js. Covers the issues most commonly flagged in code review: missing form labels, incorrect ARIA usage, non-semantic interactive elements, and broken keyboard navigation.
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## When to Activate
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- Building or reviewing form components (`<input>`, `<select>`, `<textarea>`)
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- Creating interactive elements (modals, dropdowns, tooltips, tabs)
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- Using `<div>` or `<span>` with `onClick`
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- Adding `aria-*` attributes to any element
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- Implementing keyboard navigation or focus management
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- Receiving accessibility feedback from code review tools (CodeRabbit, ESLint a11y)
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- Building components that must support screen readers
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## Form Accessibility
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Missing `htmlFor` / `id` pairing and disconnected error messages are the most common issues flagged in code review.
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### Label Connection
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```tsx
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// BAD: label has no connection to input — screen readers cannot associate them
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<label>Email</label>
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<input type="email" />
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// GOOD: htmlFor matches input id
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<label htmlFor="email">Email</label>
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<input id="email" type="email" />
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```
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### Required Fields
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```tsx
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// BAD: visual-only asterisk conveys nothing to screen readers
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<label htmlFor="email">Email *</label>
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<input id="email" type="email" />
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// GOOD: required enables native browser validation; aria-required signals it to screen readers
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<label htmlFor="email">
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Email <span aria-hidden="true">*</span>
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</label>
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<input id="email" type="email" required aria-required="true" />
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```
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### Error Messages
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```tsx
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// BAD: error text exists visually but is not linked to the input
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<input id="email" type="email" />
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<span className="error">Invalid email address</span>
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// GOOD: aria-describedby connects input to its error message
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// aria-invalid signals the invalid state to screen readers
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<input
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id="email"
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type="email"
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aria-describedby="email-error"
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aria-invalid={!!error}
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/>
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{error && (
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<span id="email-error" role="alert">
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{error}
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</span>
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)}
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```
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### Complete Accessible Form
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```tsx
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interface LoginFormProps {
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onSubmit: (email: string, password: string) => void;
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}
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export function LoginForm({ onSubmit }: LoginFormProps) {
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const [email, setEmail] = useState('');
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const [password, setPassword] = useState('');
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const [errors, setErrors] = useState<{ email?: string; password?: string }>({});
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const handleSubmit = (e: React.FormEvent) => {
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e.preventDefault();
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const newErrors: typeof errors = {};
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if (!email) newErrors.email = 'Email is required';
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if (!password) newErrors.password = 'Password is required';
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if (Object.keys(newErrors).length) {
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setErrors(newErrors);
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return;
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}
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onSubmit(email, password);
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};
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return (
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<form onSubmit={handleSubmit} noValidate>
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<div>
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<label htmlFor="email">
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Email <span aria-hidden="true">*</span>
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</label>
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<input
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id="email"
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type="email"
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value={email}
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onChange={e => setEmail(e.target.value)}
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aria-required="true"
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aria-describedby={errors.email ? 'email-error' : undefined}
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aria-invalid={!!errors.email}
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autoComplete="email"
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/>
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{errors.email && (
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<span id="email-error" role="alert">
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{errors.email}
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</span>
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)}
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</div>
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<div>
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<label htmlFor="password">
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Password <span aria-hidden="true">*</span>
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</label>
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<input
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id="password"
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type="password"
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value={password}
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onChange={e => setPassword(e.target.value)}
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aria-required="true"
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aria-describedby={errors.password ? 'password-error' : undefined}
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aria-invalid={!!errors.password}
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autoComplete="current-password"
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/>
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{errors.password && (
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<span id="password-error" role="alert">
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{errors.password}
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</span>
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)}
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</div>
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<button type="submit">Log in</button>
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</form>
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);
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}
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```
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## Semantic HTML
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Use the element that matches the intent. Screen readers and keyboard users depend on native semantics.
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```tsx
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// BAD: div has no role, no keyboard support, no accessible name
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<div onClick={handleClick}>Submit</div>
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// GOOD: button is focusable, activates on Enter/Space, announces as "button"
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<button type="button" onClick={handleClick}>Submit</button>
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```
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```tsx
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// BAD: non-semantic navigation
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<div onClick={() => navigate('/home')}>Home</div>
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// GOOD: anchor supports right-click, middle-click, and keyboard navigation
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<a href="/home">Home</a>
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```
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```tsx
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// BAD: heading hierarchy skipped (h1 to h4)
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<h1>Dashboard</h1>
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<h4>Recent Activity</h4>
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// GOOD: sequential heading levels
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<h1>Dashboard</h1>
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<h2>Recent Activity</h2>
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```
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## ARIA Attributes
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Use ARIA only when native HTML semantics are insufficient. Wrong ARIA is worse than no ARIA.
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### aria-label vs aria-labelledby
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```tsx
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// aria-label: inline string label — use when no visible label text exists
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<button aria-label="Close modal">
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<XIcon />
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</button>
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// aria-labelledby: references another element's text — use when a visible label exists
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<section aria-labelledby="section-title">
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<h2 id="section-title">Recent Orders</h2>
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{/* content */}
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</section>
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```
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### aria-describedby
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```tsx
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// Provides supplementary description beyond the label
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<button
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aria-describedby="delete-warning"
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onClick={handleDelete}
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>
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Delete account
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</button>
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<p id="delete-warning">This action cannot be undone.</p>
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```
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### aria-live for Dynamic Content
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```tsx
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// Use aria-live to announce content that updates without a page reload
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// polite: waits for user to finish current action before announcing
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// assertive: interrupts immediately — use only for urgent errors
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export function StatusMessage({ message, isError }: { message: string; isError?: boolean }) {
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return (
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<div role="status" aria-live={isError ? 'assertive' : 'polite'} aria-atomic="true">
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{message}
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</div>
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);
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}
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```
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### aria-expanded and aria-controls
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```tsx
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export function Accordion({ title, children }: { title: string; children: React.ReactNode }) {
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const [isOpen, setIsOpen] = useState(false);
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const contentId = useId();
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return (
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<div>
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<button aria-expanded={isOpen} aria-controls={contentId} onClick={() => setIsOpen(prev => !prev)}>
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{title}
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</button>
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<div id={contentId} hidden={!isOpen}>
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{children}
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</div>
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</div>
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);
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}
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```
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## Keyboard Navigation
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Every interactive element must be reachable and operable by keyboard alone.
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### Custom Dropdown
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```tsx
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export function Dropdown({ options, onSelect }: { options: string[]; onSelect: (value: string) => void }) {
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const [isOpen, setIsOpen] = useState(false);
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const [activeIndex, setActiveIndex] = useState(0);
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const listId = useId();
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if (!options.length) return null;
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const handleKeyDown = (e: React.KeyboardEvent) => {
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switch (e.key) {
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case 'ArrowDown':
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e.preventDefault();
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setActiveIndex(i => Math.min(i + 1, options.length - 1));
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break;
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case 'ArrowUp':
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e.preventDefault();
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setActiveIndex(i => Math.max(i - 1, 0));
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break;
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case 'Enter':
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case ' ':
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e.preventDefault();
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if (isOpen) onSelect(options[activeIndex]);
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setIsOpen(prev => !prev);
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break;
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case 'Escape':
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setIsOpen(false);
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break;
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}
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};
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return (
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<div
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role="combobox"
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aria-expanded={isOpen}
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aria-haspopup="listbox"
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aria-controls={listId}
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tabIndex={0}
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onKeyDown={handleKeyDown}
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onClick={() => setIsOpen(prev => !prev)}
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>
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<span>{options[activeIndex]}</span>
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{isOpen && (
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<ul id={listId} role="listbox">
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{options.map((option, index) => (
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<li
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key={option}
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role="option"
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aria-selected={index === activeIndex}
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onClick={() => {
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onSelect(option);
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setIsOpen(false);
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}}
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>
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{option}
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</li>
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))}
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</ul>
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)}
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</div>
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);
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}
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```
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## Focus Management
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Focus must move logically when UI state changes — especially for modals and route transitions.
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### Modal Focus Restoration
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> This example covers initial focus and restoration. For a full focus trap (Tab/Shift+Tab cycling within the modal), use a library like [`focus-trap-react`](https://github.com/focus-trap/focus-trap-react) which handles edge cases like dynamic content and nested portals.
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```tsx
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export function Modal({ isOpen, onClose, title, children }: { isOpen: boolean; onClose: () => void; title: string; children: React.ReactNode }) {
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const modalRef = useRef<HTMLDivElement>(null);
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const previousFocusRef = useRef<HTMLElement | null>(null);
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useEffect(() => {
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if (isOpen) {
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// Save currently focused element and move focus into modal
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previousFocusRef.current = document.activeElement as HTMLElement;
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modalRef.current?.focus();
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} else {
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// Restore focus to the element that opened the modal
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previousFocusRef.current?.focus();
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}
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}, [isOpen]);
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if (!isOpen) return null;
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return (
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<div ref={modalRef} role="dialog" aria-modal="true" aria-labelledby="modal-title" tabIndex={-1} onKeyDown={e => e.key === 'Escape' && onClose()}>
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<h2 id="modal-title">{title}</h2>
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{children}
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<button onClick={onClose}>Close</button>
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</div>
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);
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}
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```
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## Images and Icons
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```tsx
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// BAD: decorative icon announced as unlabeled image
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<img src="/icon.svg" />
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// GOOD: decorative image hidden from screen readers
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<img src="/decoration.png" alt="" aria-hidden="true" />
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// GOOD: meaningful image with descriptive alt text
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<img src="/chart.png" alt="Monthly revenue increased 23% from January to March" />
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// GOOD: icon button with accessible label
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<button aria-label="Delete item">
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<TrashIcon aria-hidden="true" />
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</button>
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```
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## Reduced Motion
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Respect users who have requested reduced motion in their OS settings.
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```tsx
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export function useReducedMotion(): boolean {
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const [prefersReduced, setPrefersReduced] = useState(false);
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useEffect(() => {
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const mq = window.matchMedia('(prefers-reduced-motion: reduce)');
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setPrefersReduced(mq.matches);
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const handler = (e: MediaQueryListEvent) => setPrefersReduced(e.matches);
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mq.addEventListener('change', handler);
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return () => mq.removeEventListener('change', handler);
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}, []);
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return prefersReduced;
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}
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// Usage
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export function AnimatedCard({ children }: { children: React.ReactNode }) {
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const reduceMotion = useReducedMotion();
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return (
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<div
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style={{
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transition: reduceMotion ? 'none' : 'transform 300ms ease'
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}}
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>
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{children}
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</div>
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);
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}
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```
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## Anti-Patterns
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```tsx
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// BAD: onClick on non-interactive element with no keyboard support
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<div onClick={handleClick}>Click me</div>
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// BAD: aria-label on a div that has no role
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<div aria-label="Navigation">...</div>
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// BAD: placeholder used as a substitute for label
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<input placeholder="Enter your email" />
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// BAD: positive tabIndex creates unpredictable tab order
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<button tabIndex={3}>Submit</button>
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// BAD: aria-hidden on a focusable element — keyboard users get trapped
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<button aria-hidden="true">Open</button>
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// BAD: role="button" on div without keyboard handler
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<div role="button" onClick={handleClick}>Submit</div>
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// Missing: tabIndex={0}, onKeyDown for Enter/Space
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```
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## Checklist
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Before submitting any interactive component for review:
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- [ ] Every `<input>`, `<select>`, and `<textarea>` has a connected `<label>` via `htmlFor`/`id`
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- [ ] Error messages are linked with `aria-describedby` and marked `role="alert"`
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- [ ] No `onClick` on `<div>` or `<span>` without `role`, `tabIndex`, and `onKeyDown`
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- [ ] Icon-only buttons have `aria-label`
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- [ ] Decorative images use `alt=""` and `aria-hidden="true"`
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- [ ] Modals restore focus on close (for full focus trapping with Tab/Shift+Tab cycling, use a library like `focus-trap-react`)
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- [ ] Dynamic content updates use `aria-live`
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- [ ] `prefers-reduced-motion` is respected for animations
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## Related Skills
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- `frontend-patterns` — general React component and state patterns
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- `design-system` — design token and component consistency
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- `motion-ui` — animation patterns with accessibility considerations
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