wcag-audit-patterns（WCAG 审核模式）

WCAG Audit Patterns

Comprehensive guide to auditing web content against WCAG 2.2 guidelines with actionable remediation strategies.

When to Use This Skill

• Conducting accessibility audits
• Fixing WCAG violations
• Implementing accessible components
• Preparing for accessibility lawsuits
• Meeting ADA/Section 508 requirements
• Achieving VPAT compliance

Core Concepts

1. WCAG Conformance Levels

2. POUR Principles

Perceivable:  Can users perceive the content?
Operable:     Can users operate the interface?
Understandable: Can users understand the content?
Robust:       Does it work with assistive tech?

3. Common Violations by Impact

Critical (Blockers):
├── Missing alt text for functional images
├── No keyboard access to interactive elements
├── Missing form labels
└── Auto-playing media without controls

Serious:
├── Insufficient color contrast
├── Missing skip links
├── Inaccessible custom widgets
└── Missing page titles

Moderate:
├── Missing language attribute
├── Unclear link text
├── Missing landmarks
└── Improper heading hierarchy

Audit Checklist

Perceivable (Principle 1)

## 1.1 Text Alternatives

### 1.1.1 Non-text Content (Level A)

- [ ] All images have alt text
- [ ] Decorative images have alt=""
- [ ] Complex images have long descriptions
- [ ] Icons with meaning have accessible names
- [ ] CAPTCHAs have alternatives

Check:

<!-- Good --> <img src="chart.png" alt="Sales increased 25% from Q1 to Q2" /> <img src="decorative-line.png" alt="" />

<!-- Bad --> <img src="chart.png" /> <img src="decorative-line.png" alt="decorative line" />

1.2 Time-based Media

1.2.1 Audio-only and Video-only (Level A)

• Audio has text transcript
• Video has audio description or transcript

1.2.2 Captions (Level A)

• All video has synchronized captions
• Captions are accurate and complete
• Speaker identification included

1.2.3 Audio Description (Level A)

• Video has audio description for visual content

1.3 Adaptable

1.3.1 Info and Relationships (Level A)

• Headings use proper tags (h1-h6)
• Lists use ul/ol/dl
• Tables have headers
• Form inputs have labels
• ARIA landmarks present

Check:

<!-- Heading hierarchy -->
<h1>Page Title</h1>
<h2>Section</h2>
<h3>Subsection</h3>
<h2>Another Section</h2>

<!-- Table headers -->
<table>
  <thead>
    <tr>
      <th scope="col">Name</th>
      <th scope="col">Price</th>
    </tr>
  </thead>
</table>

1.3.2 Meaningful Sequence (Level A)

• Reading order is logical
• CSS positioning doesn't break order
• Focus order matches visual order

1.3.3 Sensory Characteristics (Level A)

• Instructions don't rely on shape/color alone
• "Click the red button" → "Click Submit (red button)"

1.4 Distinguishable

1.4.1 Use of Color (Level A)

• Color is not only means of conveying info
• Links distinguishable without color
• Error states not color-only

1.4.3 Contrast (Minimum) (Level AA)

• Text: 4.5:1 contrast ratio
• Large text (18pt+): 3:1 ratio
• UI components: 3:1 ratio

Tools: WebAIM Contrast Checker, axe DevTools

1.4.4 Resize Text (Level AA)

• Text resizes to 200% without loss
• No horizontal scrolling at 320px
• Content reflows properly

1.4.10 Reflow (Level AA)

• Content reflows at 400% zoom
• No two-dimensional scrolling
• All content accessible at 320px width

1.4.11 Non-text Contrast (Level AA)

• UI components have 3:1 contrast
• Focus indicators visible
• Graphical objects distinguishable

1.4.12 Text Spacing (Level AA)

• No content loss with increased spacing
• Line height 1.5x font size
• Paragraph spacing 2x font size
• Letter spacing 0.12x font size
• Word spacing 0.16x font size

### Operable (Principle 2)

2.1 Keyboard Accessible

2.1.1 Keyboard (Level A)

• [ ] All functionality keyboard accessible
• [ ] No keyboard traps
• [ ] Tab order is logical
• [ ] Custom widgets are keyboard operable

Check:

// Custom button must be keyboard accessible
<div role="button" tabindex="0"
     onkeydown="if(event.key === 'Enter' || event.key === ' ') activate()">

2.1.2 No Keyboard Trap (Level A)

• Focus can move away from all components
• Modal dialogs trap focus correctly
• Focus returns after modal closes

2.2 Enough Time

2.2.1 Timing Adjustable (Level A)

• Session timeouts can be extended
• User warned before timeout
• Option to disable auto-refresh

2.2.2 Pause, Stop, Hide (Level A)

• Moving content can be paused
• Auto-updating content can be paused
• Animations respect prefers-reduced-motion

@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}

2.3 Seizures and Physical Reactions

2.3.1 Three Flashes (Level A)

• No content flashes more than 3 times/second
• Flashing area is small (<25% viewport)

2.4 Navigable

2.4.1 Bypass Blocks (Level A)

• Skip to main content link present
• Landmark regions defined
• Proper heading structure

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

2.4.2 Page Titled (Level A)

• Unique, descriptive page titles
• Title reflects page content

2.4.3 Focus Order (Level A)

• Focus order matches visual order
• tabindex used correctly

2.4.4 Link Purpose (In Context) (Level A)

• Links make sense out of context
• No "click here" or "read more" alone

<!-- Bad -->
<a href="report.pdf">Click here</a>

<!-- Good -->
<a href="report.pdf">Download Q4 Sales Report (PDF)</a>

2.4.6 Headings and Labels (Level AA)

• Headings describe content
• Labels describe purpose

2.4.7 Focus Visible (Level AA)

• Focus indicator visible on all elements
• Custom focus styles meet contrast

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

2.4.11 Focus Not Obscured (Level AA) - WCAG 2.2

• Focused element not fully hidden
• Sticky headers don't obscure focus

### Understandable (Principle 3)

3.1 Readable

3.1.1 Language of Page (Level A)

• [ ] HTML lang attribute set
• [ ] Language correct for content

<html lang="en">

3.1.2 Language of Parts (Level AA)

• Language changes marked

<p>The French word <span lang="fr">bonjour</span> means hello.</p>

3.2 Predictable

3.2.1 On Focus (Level A)

• No context change on focus alone
• No unexpected popups on focus

3.2.2 On Input (Level A)

• No automatic form submission
• User warned before context change

3.2.3 Consistent Navigation (Level AA)

• Navigation consistent across pages
• Repeated components same order

3.2.4 Consistent Identification (Level AA)

• Same functionality = same label
• Icons used consistently

3.3 Input Assistance

3.3.1 Error Identification (Level A)

• Errors clearly identified
• Error message describes problem
• Error linked to field

<input aria-describedby="email-error" aria-invalid="true" />
<span id="email-error" role="alert">Please enter valid email</span>

3.3.2 Labels or Instructions (Level A)

• All inputs have visible labels
• Required fields indicated
• Format hints provided

3.3.3 Error Suggestion (Level AA)

• Errors include correction suggestion
• Suggestions are specific

3.3.4 Error Prevention (Level AA)

• Legal/financial forms reversible
• Data checked before submission
• User can review before submit

### Robust (Principle 4)

4.1 Compatible

4.1.1 Parsing (Level A) - Obsolete in WCAG 2.2

• [ ] Valid HTML (good practice)
• [ ] No duplicate IDs
• [ ] Complete start/end tags

4.1.2 Name, Role, Value (Level A)

• [ ] Custom widgets have accessible names
• [ ] ARIA roles correct
• [ ] State changes announced

<!-- Accessible custom checkbox -->
<div role="checkbox"
     aria-checked="false"
     tabindex="0"
     aria-labelledby="label">
</div>
<span id="label">Accept terms</span>

4.1.3 Status Messages (Level AA)

• Status updates announced
• Live regions used correctly

<div role="status" aria-live="polite">3 items added to cart</div>

<div role="alert" aria-live="assertive">Error: Form submission failed</div>

## Automated Testing

// axe-core integration const axe = require('axe-core');

async function runAccessibilityAudit(page) { await page.addScriptTag({ path: require.resolve('axe-core') });

const results = await page.evaluate(async () => { return await axe.run(document, { runOnly: { type: 'tag', values: ['wcag2a', 'wcag2aa', 'wcag21aa', 'wcag22aa'] } }); });

return { violations: results.violations, passes: results.passes, incomplete: results.incomplete }; }

// Playwright test example test('should have no accessibility violations', async ({ page }) => { await page.goto('/'); const results = await runAccessibilityAudit(page);

expect(results.violations).toHaveLength(0); });

CLI tools

npx @axe-core/cli https://example.com npx pa11y https://example.com lighthouse https://example.com --only-categories=accessibility

## Remediation Patterns

### Fix: Missing Form Labels

<!-- Before --> <input type="email" placeholder="Email" />

<!-- After: Option 1 - Visible label --> <label for="email">Email address</label> <input id="email" type="email" />

<!-- After: Option 2 - aria-label --> <input type="email" aria-label="Email address" />

<!-- After: Option 3 - aria-labelledby --> <span id="email-label">Email</span> <input type="email" aria-labelledby="email-label" />

### Fix: Insufficient Color Contrast

/* Before: 2.5:1 contrast */ .text { color: #767676; }

/* After: 4.5:1 contrast */ .text { color: #595959; }

/* Or add background */ .text { color: #767676; background: #000; }

### Fix: Keyboard Navigation

// Make custom element keyboard accessible class AccessibleDropdown extends HTMLElement { connectedCallback() { this.setAttribute("tabindex", "0"); this.setAttribute("role", "combobox"); this.setAttribute("aria-expanded", "false");

this.addEventListener("keydown", (e) => { switch (e.key) { case "Enter": case " ": this.toggle(); e.preventDefault(); break; case "Escape": this.close(); break; case "ArrowDown": this.focusNext(); e.preventDefault(); break; case "ArrowUp": this.focusPrevious(); e.preventDefault(); break; } }); } }

## Best Practices

### Do's

- **Start early** - Accessibility from design phase
- **Test with real users** - Disabled users provide best feedback
- **Automate what you can** - 30-50% issues detectable
- **Use semantic HTML** - Reduces ARIA needs
- **Document patterns** - Build accessible component library

### Don'ts

- **Don't rely only on automated testing** - Manual testing required
- **Don't use ARIA as first solution** - Native HTML first
- **Don't hide focus outlines** - Keyboard users need them
- **Don't disable zoom** - Users need to resize
- **Don't use color alone** - Multiple indicators needed

## Resources

- [WCAG 2.2 Guidelines](https://www.w3.org/TR/WCAG22/)
- [WebAIM](https://webaim.org/)
- [A11y Project Checklist](https://www.a11yproject.com/checklist/)
- [axe DevTools](https://www.deque.com/axe/)