accessibility-implementation

---
name: accessibility-implementation
description: WCAG 2.1/2.2 compliance, ARIA patterns, keyboard nav, focus management, a11y testing. Use when implementing accessible components or user mentions WCAG/ARIA/screen readers.
license: MIT
---

# Accessibility Implementation

Technical implementation of WCAG guidelines, ARIA patterns, and assistive technology support.

## When to Use This Skill

| Use this skill when... | Use design-tokens instead when... |
|---|---|
| Implementing WCAG 2.1/2.2 success criteria in code | Setting up CSS custom properties or theme systems |
| Adding ARIA roles, states, or live regions | Defining semantic colour tokens used by themes |
| Wiring keyboard navigation, focus traps, or skip links | Organizing primitive/semantic/component token tiers |
| Auditing components with axe-core, jest-axe, or Playwright | Implementing light/dark mode token overrides |

## Core Expertise

- **WCAG Compliance**: Implementing WCAG 2.1/2.2 success criteria in code
- **ARIA Patterns**: Correct usage of roles, states, and properties
- **Keyboard Navigation**: Focus management, key handlers, logical tab order
- **Screen Readers**: Content structure, announcements, live regions
- **Testing**: Automated and manual accessibility testing

## WCAG Quick Reference

### Level A (Must Have)

| Criterion | Implementation |
|-----------|----------------|
| 1.1.1 Non-text Content | `alt` for images, labels for inputs |
| 1.3.1 Info and Relationships | Semantic HTML, ARIA relationships |
| 2.1.1 Keyboard | All interactive elements keyboard accessible |
| 2.4.1 Bypass Blocks | Skip links, landmarks |
| 4.1.2 Name, Role, Value | ARIA labels, roles for custom widgets |

### Level AA (Should Have)

| Criterion | Implementation |
|-----------|----------------|
| 1.4.3 Contrast (Minimum) | 4.5:1 text, 3:1 large text |
| 1.4.11 Non-text Contrast | 3:1 for UI components |
| 2.4.6 Headings and Labels | Descriptive, hierarchical headings |
| 2.4.7 Focus Visible | Visible focus indicator (2px+ outline) |

## ARIA Patterns

### Buttons and Links

```html
<!-- Custom button -->
<div role="button" tabindex="0"
     aria-pressed="false"
     onkeydown="handleKeyDown(event)">
  Toggle Feature
</div>

<!-- Icon button (needs accessible name) -->
<button aria-label="Close dialog">
  <svg aria-hidden="true">...</svg>
</button>

<!-- Link vs button -->
<!-- Use link for navigation, button for actions -->
<a href="/page">Go to page</a>
<button type="button">Submit form</button>
```

### Form Controls

```html
<!-- Input with label -->
<label for="email">Email address</label>
<input id="email" type="email"
       aria-describedby="email-hint email-error"
       aria-invalid="true"
       required>
<div id="email-hint">We'll never share your email</div>
<div id="email-error" role="alert">Please enter a valid email</div>

<!-- Checkbox group -->
<fieldset>
  <legend>Notification preferences</legend>
  <label><input type="checkbox" name="notif" value="email"> Email</label>
  <label><input type="checkbox" name="notif" value="sms"> SMS</label>
</fieldset>

<!-- Combobox (autocomplete) -->
<label for="country">Country</label>
<input id="country"
       role="combobox"
       aria-expanded="false"
       aria-autocomplete="list"
       aria-controls="country-listbox">
<ul id="country-listbox" role="listbox" hidden>
  <li role="option" id="opt-us">United States</li>
  <li role="option" id="opt-uk">United Kingdom</li>
</ul>
```

### Modal Dialog

```html
<div role="dialog"
     aria-modal="true"
     aria-labelledby="dialog-title"
     aria-describedby="dialog-desc">
  <h2 id="dialog-title">Confirm Action</h2>
  <p id="dialog-desc">Are you sure you want to proceed?</p>
  <button>Cancel</button>
  <button>Confirm</button>
</div>
```

```typescript
// Focus trap implementation
function trapFocus(dialog: HTMLElement) {
  const focusable = dialog.querySelectorAll(
    'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
  );
  const first = focusable[0] as HTMLElement;
  const last = focusable[focusable.length - 1] as HTMLElement;

  dialog.addEventListener('keydown', (e) => {
    if (e.key === 'Tab') {
      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    }
    if (e.key === 'Escape') {
      closeDialog();
    }
  });

  // Move focus to first element
  first.focus();
}
```

### Tabs

```html
<div role="tablist" aria-label="Settings tabs">
  <button role="tab"
          id="tab-1"
          aria-selected="true"
          aria-controls="panel-1">
    General
  </button>
  <button role="tab"
          id="tab-2"
          aria-selected="false"
          aria-controls="panel-2"
          tabindex="-1">
    Privacy
  </button>
</div>

<div role="tabpanel" id="panel-1" aria-labelledby="tab-1">
  General settings content
</div>
<div role="tabpanel" id="panel-2" aria-labelledby="tab-2" hidden>
  Privacy settings content
</div>
```

```typescript
// Tab keyboard navigation
tablist.addEventListener('keydown', (e) => {
  const tabs = Array.from(tablist.querySelectorAll('[role="tab"]'));
  const current = tabs.indexOf(document.activeElement as Element);

  let next: number;
  switch (e.key) {
    case 'ArrowRight':
      next = (current + 1) % tabs.length;
      break;
    case 'ArrowLeft':
      next = (current - 1 + tabs.length) % tabs.length;
      break;
    case 'Home':
      next = 0;
      break;
    case 'End':
      next = tabs.length - 1;
      break;
    default:
      return;
  }

  e.preventDefault();
  (tabs[next] as HTMLElement).focus();
  activateTab(tabs[next]);
});
```

### Live Regions

```html
<!-- Status messages -->
<div role="status" aria-live="polite">
  Form saved successfully
</div>

<!-- Alerts (interrupts) -->
<div role="alert" aria-live="assertive">
  Error: Connection lost
</div>

<!-- Progress updates -->
<div aria-live="polite" aria-atomic="true">
  Loading: 45% complete
</div>
```

## Keyboard Navigation

### Standard Key Bindings

| Key | Behavior |
|-----|----------|
| Tab | Move to next focusable element |
| Shift+Tab | Move to previous focusable element |
| Enter/Space | Activate button, select option |
| Escape | Close modal, cancel operation |
| Arrow keys | Navigate within component (tabs, menu, listbox) |
| Home/End | Go to first/last item in list |

### Focus Management

```typescript
// Return focus after modal close
const triggerElement = document.activeElement;
openModal();
// On close:
closeModal();
triggerElement?.focus();

// Move focus to error
function showValidationErrors() {
  const firstError = document.querySelector('[aria-invalid="true"]');
  (firstError as HTMLElement)?.focus();
}

// Skip link
<a href="#main-content" class="skip-link">Skip to main content</a>
<main id="main-content" tabindex="-1">...</main>
```

### Roving Tabindex

```typescript
// For composite widgets (toolbar, menu, tabs)
function setRovingTabindex(container: HTMLElement, selector: string) {
  const items = container.querySelectorAll(selector);

  items.forEach((item, index) => {
    item.setAttribute('tabindex', index === 0 ? '0' : '-1');
  });

  container.addEventListener('keydown', (e) => {
    const current = Array.from(items).indexOf(document.activeElement as Element);
    let next = current;

    if (e.key === 'ArrowRight' || e.key === 'ArrowDown') {
      next = (current + 1) % items.length;
    } else if (e.key === 'ArrowLeft' || e.key === 'ArrowUp') {
      next = (current - 1 + items.length) % items.length;
    }

    if (next !== current) {
      items[current].setAttribute('tabindex', '-1');
      items[next].setAttribute('tabindex', '0');
      (items[next] as HTMLElement).focus();
      e.preventDefault();
    }
  });
}
```

## Testing

### Automated Testing

```bash
# axe-core CLI
npx @axe-core/cli https://localhost:3000

# Lighthouse accessibility audit
npx lighthouse http://localhost:3000 --only-categories=accessibility --output=json

# pa11y
npx pa11y http://localhost:3000

# jest-axe for unit tests
npm install --save-dev jest-axe
```

```typescript
// jest-axe example
import { axe, toHaveNoViolations } from 'jest-axe';

expect.extend(toHaveNoViolations);

test('component is accessible', async () => {
  const { container } = render(<MyComponent />);
  const results = await axe(container);
  expect(results).toHaveNoViolations();
});
```

```typescript
// Playwright accessibility testing
import { test, expect } from '@playwright/test';
import AxeBuilder from '@axe-core/playwright';

test('page should not have accessibility violations', async ({ page }) => {
  await page.goto('/');

  const results = await new AxeBuilder({ page })
    .withTags(['wcag2a', 'wcag2aa'])
    .analyze();

  expect(results.violations).toEqual([]);
});
```

### Manual Testing Checklist

**Keyboard Navigation**
- [ ] All interactive elements reachable via Tab
- [ ] Focus order matches visual order
- [ ] Focus indicator always visible
- [ ] No keyboard traps
- [ ] Escape closes modals/menus

**Screen Reader Testing**
- [ ] VoiceOver (macOS): Cmd+F5
- [ ] NVDA (Windows): Free download
- [ ] Test: Links announce destination
- [ ] Test: Forms announce labels and errors
- [ ] Test: Dynamic content announced

**Visual Testing**
- [ ] Zoom to 200% without horizontal scroll
- [ ] Color contrast meets ratios
- [ ] Information not conveyed by color alone
- [ ] Focus indicators visible in all themes

## Common Fixes

### Missing Accessible Name

```html
<!-- Bad: Icon button without label -->
<button><svg>...</svg></button>

<!-- Good: Add aria-label -->
<button aria-label="Close">
  <svg aria-hidden="true">...</svg>
</button>
```

### Missing Form Labels

```html
<!-- Bad: Placeholder as label -->
<input placeholder="Email">

<!-- Good: Proper label -->
<label for="email">Email</label>
<input id="email" type="email">

<!-- Good: Visually hidden label -->
<label for="search" class="visually-hidden">Search</label>
<input id="search" type="search" placeholder="Search...">
```

### Missing Heading Structure

```html
<!-- Bad: Skipping heading levels -->
<h1>Page Title</h1>
<h3>Section</h3>  <!-- Missing h2 -->

<!-- Good: Proper hierarchy -->
<h1>Page Title</h1>
<h2>Section</h2>
<h3>Subsection</h3>
```

### Focus Not Visible

```css
/* Bad: Removing focus outline */
button:focus { outline: none; }

/* Good: Custom focus indicator */
button:focus-visible {
  outline: 2px solid #0066cc;
  outline-offset: 2px;
}
```

### Color Contrast

```css
/* Bad: Low contrast */
.text { color: #999; background: #fff; } /* 2.85:1 ratio */

/* Good: Sufficient contrast */
.text { color: #595959; background: #fff; } /* 4.56:1 ratio */
```

## CSS Utilities

```css
/* Visually hidden but accessible */
.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Skip link */
.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  padding: 8px;
  background: #000;
  color: #fff;
  z-index: 100;
}

.skip-link:focus {
  top: 0;
}

/* Reduced motion */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    transition-duration: 0.01ms !important;
  }
}
```

## Best Practices

### Semantic HTML First
Use native HTML elements before ARIA. A `<button>` is better than `<div role="button">`.

### Don't Override Default Behavior
Native elements have built-in accessibility. Don't break it with JavaScript.

### Test with Real Users
Automated tools catch ~30% of issues. Manual testing with assistive technology is essential.

### Provide Multiple Ways
Offer keyboard, mouse, and touch alternatives for all interactions.

## References

- WCAG 2.1 Guidelines: https://www.w3.org/WAI/WCAG21/quickref/
- ARIA Authoring Practices: https://www.w3.org/WAI/ARIA/apg/
- axe-core Rules: https://dequeuniversity.com/rules/axe/
- A11y Project Checklist: https://www.a11yproject.com/checklist/