accessibility

分类: 测试与安全 | 上传者: cosmix | 下载: 0 | 版本: v1.0（最新）
Web accessibility patterns, WCAG compliance, and inclusive design. Use when implementing accessible UI, keyboard navigation, screen reader support, focus management, semantic HTML, or auditing for compliance. Triggers: accessibility, a11y, WCAG, ARIA, screen reader, keyboard navigation, focus, tab order, tabindex, alt text, color contrast, semantic HTML, landmark, role, aria-label, aria-labelledby, aria-describedby, aria-live, aria-expanded, aria-selected, aria-hidden, focus trap, roving tabindex, skip link, assistive technology.
更新日志: Source: GitHub https://github.com/cosmix/loom
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SKILL.md

---
name: accessibility
description: Web accessibility patterns, WCAG compliance, and inclusive design. Use when implementing accessible UI, keyboard navigation, screen reader support, focus management, semantic HTML, or auditing for compliance. Triggers: accessibility, a11y, WCAG, ARIA, screen reader, keyboard navigation, focus, tab order, tabindex, alt text, color contrast, semantic HTML, landmark, role, aria-label, aria-labelledby, aria-describedby, aria-live, aria-expanded, aria-selected, aria-hidden, focus trap, roving tabindex, skip link, assistive technology.
---

# Accessibility

## Overview

Web accessibility ensures that websites and applications are usable by everyone, including people with disabilities. This skill covers WCAG 2.1 compliance, semantic HTML, ARIA patterns, keyboard navigation, screen reader testing, visual accessibility, focus management, and automated testing.

This skill combines engineering implementation with design considerations - use when building accessible UIs, auditing compliance, or designing inclusive user experiences.

## Instructions

### 1. WCAG 2.1 Compliance Checklist

WCAG is organized around four principles (POUR):

| Principle          | Description                                       | Key Guidelines                                 |
| ------------------ | ------------------------------------------------- | ---------------------------------------------- |
| **Perceivable**    | Information must be presentable to users          | Text alternatives, captions, adaptable content |
| **Operable**       | Interface must be operable                        | Keyboard accessible, enough time, no seizures  |
| **Understandable** | Information and operation must be understandable  | Readable, predictable, input assistance        |
| **Robust**         | Content must be robust for assistive technologies | Compatible with current and future tools       |

#### Conformance Levels

- **Level A**: Minimum accessibility (must have)
- **Level AA**: Addresses major barriers (legal requirement in many jurisdictions)
- **Level AAA**: Highest level (nice to have for specific audiences)

#### Quick Compliance Checklist

**Level A (Essential):**

- All images have alt text (1.1.1)
- Videos have captions (1.2.2)
- Color is not the only visual means of conveying information (1.4.1)
- All functionality available from keyboard (2.1.1)
- Users can pause, stop, or hide moving content (2.2.2)
- Page has a title (2.4.2)
- Focus order preserves meaning (2.4.3)
- Link purpose clear from text or context (2.4.4)
- Pages have headings and labels (2.4.6)
- Forms have labels or instructions (3.3.2)
- Parsing: no duplicate IDs, proper nesting (4.1.1)
- Name, role, value available for all UI components (4.1.2)

**Level AA (Standard):**

- Captions for all live audio (1.2.4)
- Audio description for video (1.2.5)
- Contrast ratio at least 4.5:1 for normal text, 3:1 for large text (1.4.3)
- Text can be resized to 200% without loss of functionality (1.4.4)
- Images of text avoided (1.4.5)
- Multiple ways to find pages (2.4.5)
- Headings and labels describe topic or purpose (2.4.6)
- Focus visible (2.4.7)
- Language of page identified (3.1.1)
- Input errors suggested (3.3.3)
- Error prevention for legal/financial transactions (3.3.4)

**Level AAA (Enhanced):**

- Sign language interpretation for videos (1.2.6)
- Extended audio description (1.2.7)
- Contrast ratio at least 7:1 (1.4.6)
- No background audio or easy to turn off (1.4.7)
- Section headings used (2.4.10)
- Context-sensitive help available (3.3.5)

```typescript
// WCAG 2.1 checklist implementation
interface WCAGChecklistItem {
  id: string;
  level: "A" | "AA" | "AAA";
  principle: "perceivable" | "operable" | "understandable" | "robust";
  description: string;
  howToTest: string;
}

const wcagChecklist: WCAGChecklistItem[] = [
  {
    id: "1.1.1",
    level: "A",
    principle: "perceivable",
    description:
      "Non-text Content: All non-text content has a text alternative",
    howToTest: "Check all images have meaningful alt text",
  },
  {
    id: "1.4.3",
    level: "AA",
    principle: "perceivable",
    description:
      "Contrast (Minimum): Text has contrast ratio of at least 4.5:1",
    howToTest: "Use contrast checker tool on all text elements",
  },
  {
    id: "2.1.1",
    level: "A",
    principle: "operable",
    description: "Keyboard: All functionality is operable via keyboard",
    howToTest: "Tab through entire page without using mouse",
  },
  // ... additional items
];
```

### 2. Semantic HTML

```html
<!-- Bad: Non-semantic structure -->
<div class="header">
  <div class="nav">
    <div class="nav-item">Home</div>
    <div class="nav-item">About</div>
  </div>
</div>
<div class="main-content">
  <div class="article">
    <div class="title">Article Title</div>
    <div class="content">Content here...</div>
  </div>
</div>
<div class="footer">Footer content</div>

<!-- Good: Semantic structure -->
<header>
  <nav aria-label="Main navigation">
    <ul>
      <li><a href="/">Home</a></li>
      <li><a href="/about">About</a></li>
    </ul>
  </nav>
</header>
<main>
  <article>
    <h1>Article Title</h1>
    <p>Content here...</p>
  </article>
</main>
<footer>Footer content</footer>
```

#### Semantic Element Reference

```typescript
// Semantic HTML element mapping
const semanticElements = {
  // Sectioning
  header: "Introductory content, typically contains navigation",
  nav: "Navigation links",
  main: "Main content of the document (only one per page)",
  article: "Self-contained content that could be distributed independently",
  section: "Thematic grouping of content with a heading",
  aside: "Content tangentially related to the main content",
  footer: "Footer for its nearest sectioning content",

  // Text content
  h1_h6: "Heading levels (maintain hierarchy, one h1 per page)",
  p: "Paragraph",
  ul_ol: "Unordered/ordered lists",
  blockquote: "Extended quotation",
  figure: "Self-contained content with optional caption",
  figcaption: "Caption for a figure",

  // Interactive
  button: "Clickable button (not for links)",
  a: "Hyperlink to another page or resource",
  details: "Disclosure widget with summary",
  dialog: "Modal or non-modal dialog box",

  // Form elements
  form: "Interactive form",
  label: "Caption for form element (always use with inputs)",
  fieldset: "Group of related form elements",
  legend: "Caption for fieldset",
};
```

### 3. ARIA Attributes

```typescript
// ARIA roles, states, and properties

// Landmark roles
const landmarkRoles = [
  "banner", // Page header (use with <header>)
  "navigation", // Navigation (use with <nav>)
  "main", // Main content (use with <main>)
  "complementary", // Supporting content (use with <aside>)
  "contentinfo", // Footer (use with <footer>)
  "search", // Search functionality
  "form", // Form (use with <form>)
  "region", // Generic landmark (requires aria-label)
];

// Widget roles
const widgetRoles = [
  "button",
  "checkbox",
  "dialog",
  "menu",
  "menuitem",
  "progressbar",
  "slider",
  "tab",
  "tablist",
  "tabpanel",
  "tooltip",
  "tree",
  "treeitem",
];

// Common ARIA attributes
interface AriaAttributes {
  // Labels and descriptions
  "aria-label": string; // Accessible name
  "aria-labelledby": string; // ID of labelling element
  "aria-describedby": string; // ID of describing element

  // States
  "aria-expanded": boolean; // Expandable element state
  "aria-selected": boolean; // Selection state
  "aria-checked": boolean | "mixed"; // Checkbox/switch state
  "aria-pressed": boolean | "mixed"; // Toggle button state
  "aria-disabled": boolean; // Disabled state
  "aria-hidden": boolean; // Hidden from assistive tech

  // Live regions
  "aria-live": "off" | "polite" | "assertive";
  "aria-atomic": boolean;
  "aria-relevant": string;

  // Relationships
  "aria-controls": string; // ID of controlled element
  "aria-owns": string; // ID of owned elements
  "aria-haspopup": boolean | "menu" | "dialog";

  // Other
  "aria-current": "page" | "step" | "location" | "date" | "time" | boolean;
  "aria-invalid": boolean | "grammar" | "spelling";
  "aria-required": boolean;
}
```

#### ARIA Examples

```tsx
// Accessible modal dialog
function Modal({ isOpen, onClose, title, children }) {
  const titleId = useId();

  useEffect(() => {
    if (isOpen) {
      // Trap focus inside modal
      const focusableElements = modalRef.current.querySelectorAll(
        'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])',
      );
      const firstElement = focusableElements[0];
      const lastElement = focusableElements[focusableElements.length - 1];

      firstElement?.focus();

      const handleTab = (e: KeyboardEvent) => {
        if (e.key === "Tab") {
          if (e.shiftKey && document.activeElement === firstElement) {
            e.preventDefault();
            lastElement?.focus();
          } else if (!e.shiftKey && document.activeElement === lastElement) {
            e.preventDefault();
            firstElement?.focus();
          }
        }
        if (e.key === "Escape") {
          onClose();
        }
      };

      document.addEventListener("keydown", handleTab);
      return () => document.removeEventListener("keydown", handleTab);
    }
  }, [isOpen, onClose]);

  if (!isOpen) return null;

  return (
    <div
      role="dialog"
      aria-modal="true"
      aria-labelledby={titleId}
      ref={modalRef}
    >
      <h2 id={titleId}>{title}</h2>
      {children}
      <button onClick={onClose} aria-label="Close dialog">
        Close
      </button>
    </div>
  );
}

// Accessible tabs
function Tabs({ tabs }) {
  const [activeIndex, setActiveIndex] = useState(0);

  const handleKeyDown = (e: KeyboardEvent, index: number) => {
    let newIndex = index;

    switch (e.key) {
      case "ArrowRight":
        newIndex = (index + 1) % tabs.length;
        break;
      case "ArrowLeft":
        newIndex = (index - 1 + tabs.length) % tabs.length;
        break;
      case "Home":
        newIndex = 0;
        break;
      case "End":
        newIndex = tabs.length - 1;
        break;
      default:
        return;
    }

    e.preventDefault();
    setActiveIndex(newIndex);
    document.getElementById(`tab-${newIndex}`)?.focus();
  };

  return (
    <div>
      <div role="tablist" aria-label="Content tabs">
        {tabs.map((tab, index) => (
          <button
            key={index}
            id={`tab-${index}`}
            role="tab"
            aria-selected={activeIndex === index}
            aria-controls={`panel-${index}`}
            tabIndex={activeIndex === index ? 0 : -1}
            onClick={() => setActiveIndex(index)}
            onKeyDown={(e) => handleKeyDown(e, index)}
          >
            {tab.label}
          </button>
        ))}
      </div>

      {tabs.map((tab, index) => (
        <div
          key={index}
          id={`panel-${index}`}
          role="tabpanel"
          aria-labelledby={`tab-${index}`}
          hidden={activeIndex !== index}
          tabIndex={0}
        >
          {tab.content}
        </div>
      ))}
    </div>
  );
}

// Live region for dynamic updates
function Notification({ message, type }) {
  return (
    <div
      role="alert"
      aria-live={type === "error" ? "assertive" : "polite"}
      aria-atomic="true"
    >
      {message}
    </div>
  );
}
```

### 4. Keyboard Navigation

#### Standard Keyboard Patterns

| Pattern              | Keys           | Behavior                                                   |
| -------------------- | -------------- | ---------------------------------------------------------- |
| **Tab navigation**   | Tab, Shift+Tab | Move focus forward/backward through interactive elements   |
| **Arrow navigation** | Arrow keys     | Navigate within composite widgets (menus, tabs, lists)     |
| **Action keys**      | Enter, Space   | Activate buttons/links (Enter for both, Space for buttons) |
| **Escape**           | Esc            | Close dialogs, cancel operations, exit modes               |
| **Home/End**         | Home, End      | Move to first/last item in a group                         |
| **Page Up/Down**     | PgUp, PgDn     | Scroll or navigate by page                                 |
| **Type-ahead**       | Letter keys    | Find items by typing first letter                          |

#### Common Widget Patterns

**Tabs:**

- Tab: Enter tab list
- Arrow Left/Right: Navigate between tabs
- Home/End: First/last tab
- Tab: Exit to tab panel content

**Menu:**

- Arrow Up/Down: Navigate menu items
- Arrow Right: Open submenu
- Arrow Left: Close submenu
- Home/End: First/last item
- Escape: Close menu
- Letter keys: Jump to item starting with letter

**Dialog:**

- Tab/Shift+Tab: Cycle through dialog elements (focus trap)
- Escape: Close dialog
- Focus returns to trigger element on close

**Accordion:**

- Tab: Move to next accordion header
- Arrow Up/Down: Navigate accordion headers (optional)
- Enter/Space: Toggle accordion panel
- Home/End: First/last header (optional)

**Combobox:**

- Arrow Down: Open listbox
- Arrow Up/Down: Navigate options
- Enter: Select option and close
- Escape: Close without selecting
- Type-ahead: Filter/jump to options

```tsx
// Keyboard navigation utilities

// Focus management hook
function useFocusManagement() {
  const focusableSelector = [
    "a[href]",
    "button:not([disabled])",
    "input:not([disabled])",
    "select:not([disabled])",
    "textarea:not([disabled])",
    '[tabindex]:not([tabindex="-1"])',
  ].join(", ");

  const getFocusableElements = (container: HTMLElement) => {
    return Array.from(container.querySelectorAll(focusableSelector));
  };

  const trapFocus = (container: HTMLElement) => {
    const elements = getFocusableElements(container);
    const first = elements[0] as HTMLElement;
    const last = elements[elements.length - 1] as HTMLElement;

    const handleKeyDown = (e: KeyboardEvent) => {
      if (e.key !== "Tab") return;

      if (e.shiftKey) {
        if (document.activeElement === first) {
          e.preventDefault();
          last.focus();
        }
      } else {
        if (document.activeElement === last) {
          e.preventDefault();
          first.focus();
        }
      }
    };

    container.addEventListener("keydown", handleKeyDown);
    return () => container.removeEventListener("keydown", handleKeyDown);
  };

  return { getFocusableElements, trapFocus };
}

// Roving tabindex for grouped elements
function useRovingTabindex<T extends HTMLElement>(
  items: T[],
  options: { orientation: "horizontal" | "vertical" | "both" } = {
    orientation: "horizontal",
  },
) {
  const [focusedIndex, setFocusedIndex] = useState(0);

  const handleKeyDown = (e: KeyboardEvent, index: number) => {
    const { orientation } = options;
    let newIndex = index;

    const prevKeys = orientation === "vertical" ? ["ArrowUp"] : ["ArrowLeft"];
    const nextKeys =
      orientation === "vertical" ? ["ArrowDown"] : ["ArrowRight"];

    if (orientation === "both") {
      prevKeys.push("ArrowUp", "ArrowLeft");
      nextKeys.push("ArrowDown", "ArrowRight");
    }

    if (prevKeys.includes(e.key)) {
      newIndex = (index - 1 + items.length) % items.length;
    } else if (nextKeys.includes(e.key)) {
      newIndex = (index + 1) % items.length;
    } else if (e.key === "Home") {
      newIndex = 0;
    } else if (e.key === "End") {
      newIndex = items.length - 1;
    } else {
      return;
    }

    e.preventDefault();
    setFocusedIndex(newIndex);
    items[newIndex]?.focus();
  };

  return {
    focusedIndex,
    getTabIndex: (index: number) => (index === focusedIndex ? 0 : -1),
    handleKeyDown,
  };
}

// Skip link component
function SkipLink({ targetId, children = "Skip to main content" }) {
  return (
    <a
      href={`#${targetId}`}
      className="skip-link"
      style={{
        position: "absolute",
        left: "-9999px",
        top: "auto",
        width: "1px",
        height: "1px",
        overflow: "hidden",
      }}
      onFocus={(e) => {
        e.currentTarget.style.left = "0";
        e.currentTarget.style.width = "auto";
        e.currentTarget.style.height = "auto";
      }}
      onBlur={(e) => {
        e.currentTarget.style.left = "-9999px";
        e.currentTarget.style.width = "1px";
        e.currentTarget.style.height = "1px";
      }}
    >
      {children}
    </a>
  );
}
```

### 5. Screen Reader Testing

#### Screen Reader Reference

| Reader        | Platform  | Cost     | Enable         | Key Shortcuts                                                                                                   |
| ------------- | --------- | -------- | -------------- | --------------------------------------------------------------------------------------------------------------- |
| **NVDA**      | Windows   | Free     | Auto-start     | Start: NVDA+Down, Stop: Ctrl, Next heading: H, Next link: K, Next form: F, Landmarks: D, Elements list: NVDA+F7 |
| **JAWS**      | Windows   | Paid     | Auto-start     | Start: Insert+Down, Stop: Ctrl, Next heading: H, Headings list: Insert+F6                                       |
| **VoiceOver** | macOS/iOS | Built-in | Cmd+F5         | Next: VO+Right, Previous: VO+Left, Rotor: VO+U, Activate: VO+Space                                              |
| **TalkBack**  | Android   | Built-in | Settings       | Next: Swipe right, Previous: Swipe left, Activate: Double tap, Scroll: Two-finger swipe                         |
| **Narrator**  | Windows   | Built-in | Ctrl+Win+Enter | Scan mode: Caps Lock+Space, Next heading: H, Next link: K                                                       |

#### Screen Reader Testing Checklist

**Navigation:**

- Page title announces on load
- Headings create logical outline (h1 → h6 hierarchy maintained)
- Landmark regions are properly labeled (banner, navigation, main, complementary, contentinfo)
- Skip links allow bypassing repetitive content
- Focus order follows visual reading order

**Content:**

- All images have appropriate alt text (decorative images have empty alt="")
- Links have descriptive text (avoid "click here")
- Buttons clearly indicate their action
- Dynamic content updates are announced (aria-live regions)
- Tables have proper headers and captions

**Forms:**

- Form labels are properly associated with inputs
- Error messages are associated with form fields (aria-describedby)
- Required fields indicated (aria-required)
- Invalid fields indicated (aria-invalid)
- Error summary announced on submit

**Interactions:**

- Modal focus is trapped inside dialog
- Modal announces its role and label
- Keyboard shortcuts don't conflict with screen reader shortcuts
- Custom widgets announce state changes (aria-expanded, aria-selected)

```typescript
// Screen reader testing utilities

const screenReaderTesting = {
  // Common screen readers
  readers: {
    nvda: {
      platform: "Windows",
      cost: "Free",
      shortcuts: {
        startReading: "NVDA + Down Arrow",
        stopReading: "Ctrl",
        nextHeading: "H",
        nextLink: "K",
        nextFormField: "F",
        nextLandmark: "D",
        elementsList: "NVDA + F7",
      },
    },
    jaws: {
      platform: "Windows",
      cost: "Paid",
      shortcuts: {
        startReading: "Insert + Down Arrow",
        stopReading: "Ctrl",
        nextHeading: "H",
        nextLink: "Tab",
        headingsList: "Insert + F6",
      },
    },
    voiceover: {
      platform: "macOS/iOS",
      cost: "Built-in",
      shortcuts: {
        toggle: "Cmd + F5",
        nextElement: "VO + Right Arrow",
        previousElement: "VO + Left Arrow",
        rotor: "VO + U",
        activate: "VO + Space",
      },
    },
    talkback: {
      platform: "Android",
      cost: "Built-in",
      gestures: {
        nextElement: "Swipe Right",
        previousElement: "Swipe Left",
        activate: "Double Tap",
        scrollForward: "Two finger swipe up",
      },
    },
  },
};

// Announce utility for screen readers
function announce(
  message: string,
  priority: "polite" | "assertive" = "polite",
) {
  const announcer = document.createElement("div");
  announcer.setAttribute("aria-live", priority);
  announcer.setAttribute("aria-atomic", "true");
  announcer.setAttribute("class", "sr-only");
  announcer.style.cssText = `
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
  `;

  document.body.appendChild(announcer);

  // Delay to ensure screen reader picks up the change
  setTimeout(() => {
    announcer.textContent = message;
  }, 100);

  // Clean up
  setTimeout(() => {
    document.body.removeChild(announcer);
  }, 1000);
}

// Usage
announce("Form submitted successfully");
announce("Error: Please fill in all required fields", "assertive");
```

### 6. Color Contrast and Visual Accessibility

```typescript
// Color contrast utilities

function getLuminance(r: number, g: number, b: number): number {
  const [rs, gs, bs] = [r, g, b].map((c) => {
    c = c / 255;
    return c <= 0.03928 ? c / 12.92 : Math.pow((c + 0.055) / 1.055, 2.4);
  });
  return 0.2126 * rs + 0.7152 * gs + 0.0722 * bs;
}

function getContrastRatio(color1: string, color2: string): number {
  const rgb1 = hexToRgb(color1);
  const rgb2 = hexToRgb(color2);

  const l1 = getLuminance(rgb1.r, rgb1.g, rgb1.b);
  const l2 = getLuminance(rgb2.r, rgb2.g, rgb2.b);

  const lighter = Math.max(l1, l2);
  const darker = Math.min(l1, l2);

  return (lighter + 0.05) / (darker + 0.05);
}

function hexToRgb(hex: string): { r: number; g: number; b: number } {
  const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
  return result
    ? {
        r: parseInt(result[1], 16),
        g: parseInt(result[2], 16),
        b: parseInt(result[3], 16),
      }
    : { r: 0, g: 0, b: 0 };
}

function meetsWCAGContrast(
  foreground: string,
  background: string,
  level: "AA" | "AAA" = "AA",
  isLargeText: boolean = false,
): boolean {
  const ratio = getContrastRatio(foreground, background);

  const requirements = {
    AA: { normal: 4.5, large: 3 },
    AAA: { normal: 7, large: 4.5 },
  };

  const required = requirements[level][isLargeText ? "large" : "normal"];
  return ratio >= required;
}

// Usage
const passes = meetsWCAGContrast("#333333", "#ffffff", "AA");
console.log(
  `Contrast ratio: ${getContrastRatio("#333333", "#ffffff").toFixed(2)}:1`,
);

// Accessible color palette generator
function generateAccessiblePalette(
  baseColor: string,
  background: string = "#ffffff",
) {
  const shades = [];
  const rgb = hexToRgb(baseColor);

  for (let i = 0; i <= 100; i += 10) {
    const factor = i / 100;
    const shade = {
      r: Math.round(rgb.r * factor),
      g: Math.round(rgb.g * factor),
      b: Math.round(rgb.b * factor),
    };
    const hex = `#${shade.r.toString(16).padStart(2, "0")}${shade.g.toString(16).padStart(2, "0")}${shade.b.toString(16).padStart(2, "0")}`;
    const ratio = getContrastRatio(hex, background);

    shades.push({
      shade: i,
      hex,
      contrastRatio: ratio.toFixed(2),
      passesAA: ratio >= 4.5,
      passesAAA: ratio >= 7,
    });
  }

  return shades;
}

// Focus visible styles
const focusStyles = `
  /* Remove default outline */
  :focus {
    outline: none;
  }

  /* Add visible focus for keyboard users */
  :focus-visible {
    outline: 2px solid #005fcc;
    outline-offset: 2px;
  }

  /* High contrast mode support */
  @media (prefers-contrast: high) {
    :focus-visible {
      outline: 3px solid currentColor;
      outline-offset: 3px;
    }
  }

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

### 7. Automated A11y Testing Tools

```typescript
// Automated accessibility testing setup

// Jest + Testing Library
import { render, screen } from '@testing-library/react';
import { axe, toHaveNoViolations } from 'jest-axe';

expect.extend(toHaveNoViolations);

describe('Accessibility Tests', () => {
  it('should have no accessibility violations', async () => {
    const { container } = render(<MyComponent />);
    const results = await axe(container);
    expect(results).toHaveNoViolations();
  });

  it('should have accessible form', () => {
    render(<LoginForm />);

    // Check for proper labels
    expect(screen.getByLabelText('Email')).toBeInTheDocument();
    expect(screen.getByLabelText('Password')).toBeInTheDocument();

    // Check for proper roles
    expect(screen.getByRole('form')).toBeInTheDocument();
    expect(screen.getByRole('button', { name: 'Sign In' })).toBeInTheDocument();
  });

  it('should manage focus correctly', () => {
    render(<Modal isOpen={true} />);

    // First focusable element should be focused
    expect(document.activeElement).toBe(screen.getByRole('button', { name: 'Close' }));
  });
});

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

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

    const accessibilityScanResults = await new AxeBuilder({ page })
      .withTags(['wcag2a', 'wcag2aa', 'wcag21aa'])
      .analyze();

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

  test('should be navigable by keyboard', async ({ page }) => {
    await page.goto('/');

    // Tab to skip link
    await page.keyboard.press('Tab');
    await expect(page.getByText('Skip to main content')).toBeFocused();

    // Tab to navigation
    await page.keyboard.press('Tab');
    await expect(page.getByRole('link', { name: 'Home' })).toBeFocused();
  });
});

// CI/CD integration for accessibility
const accessibilityConfig = {
  // Lighthouse CI config
  lighthouse: {
    assertions: {
      'categories:accessibility': ['error', { minScore: 0.9 }],
      'color-contrast': 'error',
      'document-title': 'error',
      'html-has-lang': 'error',
      'image-alt': 'error',
      'label': 'error',
      'link-name': 'error',
      'meta-viewport': 'error',
    },
  },

  // Pa11y CI config
  pa11y: {
    standard: 'WCAG2AA',
    runners: ['axe', 'htmlcs'],
    ignore: [
      'WCAG2AA.Principle1.Guideline1_4.1_4_3.G18.Fail', // Ignore specific rules if needed
    ],
  },

  // Axe configuration
  axe: {
    runOnly: {
      type: 'tag',
      values: ['wcag2a', 'wcag2aa', 'wcag21aa', 'best-practice'],
    },
    rules: {
      'color-contrast': { enabled: true },
      'valid-lang': { enabled: true },
    },
  },
};
```

## Best Practices

1. **Start with Semantic HTML**: Proper HTML elements provide built-in accessibility. Use button for buttons, a for links, nav for navigation, etc.

2. **First Rule of ARIA**: Don't use ARIA if semantic HTML can do it. ARIA fixes what HTML can't express.

3. **Maintain Focus Management**: Ensure logical focus order, visible focus indicators, and proper focus trapping in modals.

4. **Keyboard First**: All functionality must work with keyboard only. Test by unplugging your mouse.

5. **Test with Real Tools**: Use screen readers (NVDA, VoiceOver), keyboard only, and automated tools (axe, Lighthouse).

6. **Provide Text Alternatives**: All images need alt text (or empty alt="" for decorative), videos need captions.

7. **Design for Inclusion**: Consider color blindness, low vision, motor disabilities, cognitive disabilities from the start.

8. **Progressive Enhancement**: Core functionality should work without JavaScript. Enhanced experience for capable browsers.

9. **Test Early and Often**: Accessibility is easier to build in than bolt on. Include in every code review.

10. **Learn from Users**: Include people with disabilities in user testing when possible.

## Examples

### Complete Accessible Form

```tsx
function AccessibleForm() {
  const [errors, setErrors] = useState<Record<string, string>>({});
  const errorSummaryRef = useRef<HTMLDivElement>(null);

  const handleSubmit = (e: FormEvent) => {
    e.preventDefault();
    const newErrors: Record<string, string> = {};

    // Validation
    if (!formData.email) {
      newErrors.email = "Email is required";
    }
    if (!formData.password) {
      newErrors.password = "Password is required";
    }

    if (Object.keys(newErrors).length > 0) {
      setErrors(newErrors);
      // Focus error summary for screen readers
      errorSummaryRef.current?.focus();
      announce(
        "Form has errors. Please correct them and try again.",
        "assertive",
      );
    } else {
      // Submit form
      announce("Form submitted successfully", "polite");
    }
  };

  return (
    <form onSubmit={handleSubmit} aria-labelledby="form-title" noValidate>
      <h1 id="form-title">Sign Up</h1>

      {Object.keys(errors).length > 0 && (
        <div
          ref={errorSummaryRef}
          role="alert"
          aria-labelledby="error-summary-title"
          tabIndex={-1}
          className="error-summary"
        >
          <h2 id="error-summary-title">There are errors in the form</h2>
          <ul>
            {Object.entries(errors).map(([field, message]) => (
              <li key={field}>
                <a href={`#${field}`}>{message}</a>
              </li>
            ))}
          </ul>
        </div>
      )}

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

      <div className="form-field">
        <label htmlFor="password">
          Password
          <span aria-hidden="true">*</span>
          <span className="sr-only">(required)</span>
        </label>
        <input
          type="password"
          id="password"
          name="password"
          autoComplete="new-password"
          aria-required="true"
          aria-invalid={!!errors.password}
          aria-describedby="password-hint password-error"
        />
        <span id="password-hint" className="hint">
          Must be at least 8 characters
        </span>
        {errors.password && (
          <span id="password-error" role="alert" className="error">
            {errors.password}
          </span>
        )}
      </div>

      <button type="submit">Create Account</button>
    </form>
  );
}
```

## Quick Reference

### Common ARIA Patterns Cheat Sheet

```typescript
// Button
<button type="button">Click me</button>

// Toggle button
<button aria-pressed="true">Mute</button>

// Icon button
<button aria-label="Close">×</button>

// Link that looks like button (DON'T - use button instead)
// If you must: <a href="#" role="button" aria-pressed="false">

// Disabled state
<button disabled>Cannot click</button>
<button aria-disabled="true">Visually disabled but focusable</button>

// Loading state
<button aria-busy="true">Saving...</button>

// Expandable section
<button aria-expanded="false" aria-controls="panel-id">Toggle</button>
<div id="panel-id" hidden>Content</div>

// Custom checkbox
<div role="checkbox" aria-checked="false" tabindex="0">Option</div>

// Modal dialog
<div role="dialog" aria-modal="true" aria-labelledby="title-id">
  <h2 id="title-id">Dialog Title</h2>
</div>

// Alert (announces immediately)
<div role="alert">Error: Form submission failed</div>

// Status (announces after current utterance)
<div role="status" aria-live="polite">5 new messages</div>

// Tabs
<div role="tablist">
  <button role="tab" aria-selected="true" aria-controls="panel1">Tab 1</button>
  <button role="tab" aria-selected="false" aria-controls="panel2">Tab 2</button>
</div>
<div id="panel1" role="tabpanel">Panel 1 content</div>
<div id="panel2" role="tabpanel" hidden>Panel 2 content</div>

// Form field with description and error
<label for="email">Email</label>
<input
  id="email"
  type="email"
  aria-describedby="email-hint email-error"
  aria-invalid="true"
  aria-required="true"
/>
<span id="email-hint">We'll never share your email</span>
<span id="email-error" role="alert">Please enter a valid email</span>

// Visually hidden but available to screen readers
<span className="sr-only">Screen reader only text</span>
// CSS: .sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; }

// Hidden from screen readers
<div aria-hidden="true">Decorative content</div>
```

### Alt Text Guidelines

```typescript
// Informative images - describe the information
<img src="chart.png" alt="Sales increased 25% from Q1 to Q2" />

// Functional images - describe the action
<img src="print-icon.png" alt="Print this page" />

// Decorative images - empty alt
<img src="decorative-border.png" alt="" />

// Complex images - use long description
<img
  src="complex-diagram.png"
  alt="System architecture diagram"
  aria-describedby="diagram-desc"
/>
<div id="diagram-desc">
  Detailed description: The system consists of...
</div>

// Images of text - avoid if possible, otherwise copy the text
<img src="logo.png" alt="Acme Corporation" />

// Background images - use empty alt, provide text alternative elsewhere
<div style="background-image: url(hero.jpg)" role="img" aria-label="Team celebrating">
```

### Focus Management Patterns

```typescript
// Focus trap (modal, sidebar)
// 1. Save previously focused element
const previousFocus = document.activeElement;

// 2. Focus first element in trap
modal.querySelector('button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])')?.focus();

// 3. On Tab, cycle within trap
// See useFocusManagement hook above

// 4. On close, restore focus
previousFocus?.focus();

// Roving tabindex (toolbar, menu)
// Only one item in group has tabindex="0", rest have tabindex="-1"
// Arrow keys move focus and update tabindex values
<div role="toolbar">
  <button tabindex="0">Cut</button>
  <button tabindex="-1">Copy</button>
  <button tabindex="-1">Paste</button>
</div>

// Skip link (first focusable element)
<a href="#main-content" className="skip-link">Skip to main content</a>
<main id="main-content" tabindex="-1">...</main>

// Focus management after deletion
// Focus next item, or previous if last, or container if empty
listItems.splice(index, 1);
if (listItems[index]) {
  listItems[index].focus();
} else if (listItems[index - 1]) {
  listItems[index - 1].focus();
} else {
  containerElement.focus();
}
```

### Testing Checklist

**Automated (Run on every PR):**

- axe-core (via jest-axe or @axe-core/playwright)
- Lighthouse accessibility score
- ESLint plugin: eslint-plugin-jsx-a11y

**Manual (Run before release):**

- Keyboard only navigation (unplug mouse)
- Screen reader testing (NVDA/VoiceOver)
- Browser zoom to 200%
- Color contrast checker (WCAG AA minimum)
- Tab through entire application
- Check focus indicators visible
- Test with reduced motion preference
- Test with high contrast mode

**Browser DevTools:**

- Chrome: Lighthouse, Accessibility tree view
- Firefox: Accessibility inspector
- Safari: Accessibility audit
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