wcag（WCAG 命令行）

WCAG 2.2 Accessibility

Deep Knowledge: Use mcp__documentation__fetch_docs with technology: wcag for comprehensive WCAG guidelines, success criteria, and techniques.

When NOT to Use This Skill

• Automated testing setup - Use the axe-core skill for integrating axe testing tools
• Component library accessibility - Use framework-specific skills (e.g., React, Vue) for accessible component patterns
• Design systems - Use UI library skills for pre-built accessible components
• ARIA implementation only - This skill covers broader WCAG compliance, not just ARIA

Official References

Conformance Levels

WCAG 2.2 Success Criteria Count

POUR Principles

1. Perceivable

// Text alternatives
<img src="chart.png" alt="Q3 sales increased 25% compared to Q2" />

// Decorative images
<img src="divider.png" alt="" role="presentation" />

// Color contrast (4.5:1 for normal text, 3:1 for large text)
// Use tools: WebAIM Contrast Checker, axe DevTools

2. Operable

// Skip link
<a href="#main-content" className="skip-link">
  Skip to main content
</a>

// Focus visible (2.4.7)
button:focus {
  outline: 3px solid #005fcc;
  outline-offset: 2px;
}

// Target size minimum (2.5.8) - 24x24 CSS pixels
.button {
  min-width: 44px;
  min-height: 44px;
  padding: 12px 16px;
}

3. Understandable

// Language of page (3.1.1)
<html lang="en">

// Error identification (3.3.1)
<div role="alert" aria-live="assertive">
  Email is required and must be valid
</div>

// Labels (3.3.2)
<label htmlFor="email">Email Address</label>
<input id="email" type="email" aria-describedby="email-hint" />
<span id="email-hint">We'll never share your email</span>

4. Robust

// Name, Role, Value (4.1.2)
<button aria-pressed="true" aria-label="Favorite this item">
  ★
</button>

// Custom controls
<div
  role="slider"
  aria-valuemin={0}
  aria-valuemax={100}
  aria-valuenow={50}
  aria-label="Volume"
  tabIndex={0}
/>

New in WCAG 2.2

Level AA (Required)

Level AAA

Common Patterns

Modal Dialog

function Modal({ isOpen, onClose, title, children }) {
  const modalRef = useRef<HTMLDivElement>(null);

  useEffect(() => {
    if (isOpen) {
      // Trap focus inside modal
      modalRef.current?.focus();

      // Prevent body scroll
      document.body.style.overflow = 'hidden';
    }
    return () => {
      document.body.style.overflow = '';
    };
  }, [isOpen]);

  if (!isOpen) return null;

  return (
    <div
      role="dialog"
      aria-modal="true"
      aria-labelledby="modal-title"
      ref={modalRef}
      tabIndex={-1}
      onKeyDown={(e) => e.key === 'Escape' && onClose()}
    >
      <h2 id="modal-title">{title}</h2>
      {children}
      <button onClick={onClose}>Close</button>
    </div>
  );
}

Dropdown Menu

function Dropdown({ label, items }) {
  const [isOpen, setIsOpen] = useState(false);
  const [activeIndex, setActiveIndex] = useState(-1);

  const handleKeyDown = (e: KeyboardEvent) => {
    switch (e.key) {
      case 'ArrowDown':
        e.preventDefault();
        setActiveIndex(i => Math.min(i + 1, items.length - 1));
        break;
      case 'ArrowUp':
        e.preventDefault();
        setActiveIndex(i => Math.max(i - 1, 0));
        break;
      case 'Escape':
        setIsOpen(false);
        break;
      case 'Enter':
      case ' ':
        if (activeIndex >= 0) items[activeIndex].onClick();
        break;
    }
  };

  return (
    <div onKeyDown={handleKeyDown}>
      <button
        aria-haspopup="menu"
        aria-expanded={isOpen}
        onClick={() => setIsOpen(!isOpen)}
      >
        {label}
      </button>
      {isOpen && (
        <ul role="menu">
          {items.map((item, i) => (
            <li
              key={item.id}
              role="menuitem"
              tabIndex={activeIndex === i ? 0 : -1}
              aria-current={activeIndex === i}
            >
              {item.label}
            </li>
          ))}
        </ul>
      )}
    </div>
  );
}

Form with Validation

function Form() {
  const [errors, setErrors] = useState<Record<string, string>>({});

  return (
    <form aria-describedby="form-errors">
      {Object.keys(errors).length > 0 && (
        <div id="form-errors" role="alert" aria-live="polite">
          <h2>Please fix the following errors:</h2>
          <ul>
            {Object.entries(errors).map(([field, msg]) => (
              <li key={field}>
                <a href={`#${field}`}>{msg}</a>
              </li>
            ))}
          </ul>
        </div>
      )}

      <div>
        <label htmlFor="email">
          Email <span aria-hidden="true">*</span>
          <span className="sr-only">(required)</span>
        </label>
        <input
          id="email"
          type="email"
          aria-required="true"
          aria-invalid={!!errors.email}
          aria-describedby={errors.email ? 'email-error' : undefined}
        />
        {errors.email && (
          <span id="email-error" role="alert">{errors.email}</span>
        )}
      </div>
    </form>
  );
}

Testing

Automated Testing with axe-core

// Playwright + axe
import { test, expect } from '@playwright/test';
import AxeBuilder from '@axe-core/playwright';

test('homepage has no accessibility violations', async ({ page }) => {
  await page.goto('/');

  const results = await new AxeBuilder({ page })
    .withTags(['wcag2a', 'wcag2aa', 'wcag22aa'])
    .analyze();

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

// Vitest + axe
import { axe, toHaveNoViolations } from 'jest-axe';
import { render } from '@testing-library/react';

expect.extend(toHaveNoViolations);

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

Manual Testing Checklist

## Keyboard Navigation
- [ ] Tab through all interactive elements
- [ ] Shift+Tab navigates backwards
- [ ] Enter/Space activates buttons and links
- [ ] Arrow keys work in menus, tabs, sliders
- [ ] Escape closes modals and dropdowns
- [ ] No keyboard traps

## Screen Reader
- [ ] All images have alt text
- [ ] Form fields have labels
- [ ] Headings are hierarchical (h1 > h2 > h3)
- [ ] Links are descriptive (not "click here")
- [ ] Dynamic content announced (aria-live)

## Visual
- [ ] Color contrast meets 4.5:1 (normal text)
- [ ] Color contrast meets 3:1 (large text, UI components)
- [ ] Focus indicators visible
- [ ] Content readable at 200% zoom
- [ ] No horizontal scrolling at 320px width

Tools

CSS Utilities

/* Visually hidden but accessible to screen readers */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Focus visible only for keyboard users */
:focus:not(:focus-visible) {
  outline: none;
}

:focus-visible {
  outline: 3px solid #005fcc;
  outline-offset: 2px;
}

/* Reduced motion preference */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

/* High contrast mode support */
@media (forced-colors: active) {
  .button {
    border: 2px solid currentColor;
  }
}

Checklist

Design Phase

• Color contrast meets requirements
• Touch targets 44x44 minimum (recommended)
• Focus states designed
• Error states include text, not just color

Development

• Semantic HTML used
• ARIA only when HTML insufficient
• Keyboard navigation works
• Focus management for SPAs
• Form errors accessible

Testing

• axe-core in CI pipeline
• Manual screen reader testing
• Keyboard-only navigation tested
• Zoom to 200% tested

Anti-Patterns

Quick Troubleshooting

Related Skills

• React
• Testing Library
• Playwright