アクセシビリティ監査担当者

包括的な Web アクセシビリティのテストとコンプライアンスのための指示。

メモ

  • このライブラリの例はインスピレーションを得るためのものです。プロジェクト、言語、チーム プロセスに合わせて具体的に調整することをお勧めします。
  • 特定の言語とシナリオ向けのカスタム指示のコミュニティに投稿された例については、Awesome GitHub Copilot Customizations リポジトリを参照してください。
  • カスタム指示は、作成するプラットフォームまたは IDE に応じて、さまざまなスコープにわたって適用できます。 詳しくは、「GitHub Copilot Chat の回答のカスタマイズについて」を参照してください。

次の例では、リポジトリ内の HTML ファイルにのみ適用されて、WCAG ガイドラインに従うアクセシビリティが高くてインクルーシブな HTML を生成するように GitHub Copilot をガイドする、パス固有の accessibility.instructions.md ファイルを示します。 パス固有の指示ファイルについて詳しくは、「GitHub Copilot のリポジトリ カスタム命令を追加する」をご覧ください。

Text
---
applyTo: **/*.html
---

When generating code, ensure accessibility compliance by following these priorities:

## Semantic HTML First
- Use proper semantic elements: `<nav>`, `<main>`, `<section>`, `<article>`, `<header>`, `<footer>`
- Structure headings sequentially (h1 → h2 → h3, never skip levels)
- Use one `<h1>` per page with descriptive heading text

## Essential ARIA Requirements
- Add `alt` text to all images
- Label form inputs with `<label>` or `aria-label`
- Ensure interactive elements have accessible names
- Use `aria-expanded` for collapsible content
- Add `role`, `aria-labelledby`, and `aria-describedby` when semantic HTML isn't sufficient

## Keyboard Navigation
- All interactive elements must be keyboard accessible
- Provide visible focus indicators (minimum 2px outline)
- Include skip links: `<a href="#main">Skip to main content</a>`
- Use logical tab order that matches visual layout

## Color and Contrast
- Ensure 4.5:1 contrast ratio for normal text, 3:1 for large text
- Don't rely solely on color to convey information

## Quick Test Questions
- Can you navigate the entire interface using only Tab/Shift+Tab/Enter?
- Are all images and icons properly described?
- Can screen reader users understand the content and functionality?

## Screen Reader Compatibility

**Provide descriptive text for all non-text content:**
- Images: Use alt text that describes function, not just appearance
  - Good: `alt="Submit form"`
  - Avoid: `alt="Blue button"`
- Form inputs: Associate every input with a `<label>` element
- Links: Use descriptive link text
  - Good: "Download the accessibility report (PDF, 2MB)"
  - Avoid: "Click here" or "Read more"

**Announce dynamic content updates:**
- Use `aria-live="polite"` for status updates
- Use `aria-live="assertive"` for urgent notifications
- Update screen reader users when content changes without page reload

---

## Color and Contrast Requirements

**Meet these specific contrast ratios:**
- Normal text (under 18pt): Minimum 4.5:1 contrast ratio
- Large text (18pt+ or 14pt+ bold): Minimum 3:1 contrast ratio
- UI components and graphics: Minimum 3:1 contrast ratio

**Provide multiple visual cues:**
- Use color + icon + text for status indicators
- Add patterns or textures to distinguish chart elements
- Include text labels on graphs and data visualizations

---

## Testing Integration Steps

**Include these automated checks:**
1. Run axe-core accessibility scanner in CI/CD pipeline
2. Test with lighthouse accessibility audit
3. Validate HTML markup for semantic correctness

**Perform these manual tests:**
1. Navigate entire interface using only Tab and arrow keys
2. Test with screen reader (NVDA on Windows, VoiceOver on Mac)
3. Verify 200% zoom doesn't break layout or hide content
4. Check color contrast with tools like WebAIM Color Contrast Checker

---

## Form Design Standards

**Create accessible form experiences:**
- Place labels above or to the left of form fields
- Group related fields with `<fieldset>` and `<legend>`
- Display validation errors immediately after the field with `aria-describedby`
- Use `aria-required="true"` for required fields
- Provide clear instructions before users start filling out forms

**Error message format:**
```html
<input aria-describedby="email-error" aria-invalid="true">
<div id="email-error">Please enter a valid email address</div>
```

---

**Code Generation Rule:** Always include accessibility comments explaining ARIA attributes and semantic choices. Test code with keyboard navigation before suggesting it's complete.

参考資料