APG Patterns
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Accordion

A vertically stacked set of interactive headings that each reveal a section of content.

Demo

Single Expansion (Default)

Only one panel can be expanded at a time. Opening a new panel closes the previously open one.

An accordion is a vertically stacked set of interactive headings that each reveal a section of content. They are commonly used to reduce the need to scroll when presenting multiple sections of content on a single page.

Use accordions when you need to organize content into collapsible sections. This helps reduce visual clutter while keeping information accessible. They are particularly useful for FAQs, settings panels, and navigation menus.

Accordions must be keyboard accessible and properly announce their expanded/collapsed state to screen readers. Each header should be a proper heading element, and the panel should be associated with its header via aria-controls and aria-labelledby.

Multiple Expansion

Multiple panels can be expanded simultaneously using the allowMultiple prop.

Content for section one. With allowMultiple enabled, multiple sections can be open at the same time.

Content for section two. Try opening this while section one is still open.

Content for section three. All three sections can be expanded simultaneously.

With Disabled Items

Individual accordion items can be disabled. Keyboard navigation automatically skips disabled items.

This section can be expanded and collapsed normally.

This content is not accessible because the section is disabled.

This section can also be expanded. The disabled section is removed from the Tab order, so Tab moves directly between the enabled sections.

Open demo only →

Accessibility Features

WAI-ARIA Roles

Role Target Element Description
heading Header wrapper (h2-h6) Contains the accordion trigger button
button Header trigger Interactive element that toggles panel visibility
region Panel (optional) Content area associated with header (omit for 6+ panels)

WAI-ARIA Properties

aria-level

headingLevel prop

Values
2 - 6
Required
Yes

aria-controls

Auto-generated

Values
ID reference to associated panel
Required
Yes

aria-labelledby

Auto-generated

Values
ID reference to header button
Required
Yes (if region used)

WAI-ARIA States

aria-expanded

Target Element
button element
Values
true | false
Required
Yes
Change Trigger
Click, Enter, Space

aria-disabled

Target Element
button element
Values
true | false
Required
No
Change Trigger
Only when disabled

Keyboard Support

Key Action
Tab Move focus to the next focusable element
Shift + Tab Move focus to the previous focusable element
Space / Enter Toggle the expansion of the focused accordion header
  • Header navigation uses the standard Tab order; arrow / Home / End key navigation is no longer part of the APG Accordion keyboard interaction.

Focus Management

Event Behavior
Header buttons Focusable via their button elements
Tab order Headers participate in the page Tab sequence; navigate between headers with Tab / Shift+Tab

Implementation Notes

┌─────────────────────────────────────┐
│ [▼] Section 1                       │  ← button (aria-expanded="true")
├─────────────────────────────────────┤
│ Panel 1 content...                  │  ← region (aria-labelledby)
├─────────────────────────────────────┤
│ [▶] Section 2                       │  ← button (aria-expanded="false")
├─────────────────────────────────────┤
│ [▶] Section 3                       │  ← button (aria-expanded="false")
└─────────────────────────────────────┘

ID Relationships:
- Button: id="header-1", aria-controls="panel-1"
- Panel: id="panel-1", aria-labelledby="header-1"

Region Role Rule:
- ≤6 panels: use role="region" on panels
- >6 panels: omit role="region" (too many landmarks)

Accordion component structure with ID relationships

References

Source Code

Accordion.tsx
import { useCallback, useId, useState } from 'react';

/**
 * Accordion item configuration
 * @see https://www.w3.org/WAI/ARIA/apg/patterns/accordion/
 */
export interface AccordionItem {
  /** Unique identifier for the item */
  id: string;
  /** Content displayed in the accordion header button */
  header: React.ReactNode;
  /** Content displayed in the collapsible panel */
  content: React.ReactNode;
  /** When true, the item cannot be expanded/collapsed */
  disabled?: boolean;
  /** When true, the panel is expanded on initial render */
  defaultExpanded?: boolean;
}

/**
 * Props for the Accordion component
 *
 * @example
 * ```tsx
 * const items = [
 *   { id: 'section1', header: 'Section 1', content: 'Content 1', defaultExpanded: true },
 *   { id: 'section2', header: 'Section 2', content: 'Content 2' },
 * ];
 *
 * <Accordion
 *   items={items}
 *   headingLevel={3}
 *   allowMultiple={false}
 *   onExpandedChange={(ids) => console.log('Expanded:', ids)}
 * />
 * ```
 */
export interface AccordionProps {
  /**
   * Array of accordion items to display
   * Each item requires an id, header, and content
   */
  items: AccordionItem[];
  /**
   * Allow multiple panels to be expanded simultaneously
   * @default false
   */
  allowMultiple?: boolean;
  /**
   * Heading level for accessibility (h2-h6)
   * Should match the document outline hierarchy
   * @default 3
   */
  headingLevel?: 2 | 3 | 4 | 5 | 6;
  /**
   * Callback fired when the expanded panels change
   * @param expandedIds - Array of currently expanded item IDs
   */
  onExpandedChange?: (expandedIds: string[]) => void;
  /**
   * Additional CSS class to apply to the accordion container
   * @default ""
   */
  className?: string;
}

export function Accordion({
  items,
  allowMultiple = false,
  headingLevel = 3,
  onExpandedChange,
  className = '',
}: AccordionProps): React.ReactElement {
  const instanceId = useId();

  // Initialize with defaultExpanded items
  const [expandedIds, setExpandedIds] = useState<string[]>(() =>
    items.filter((item) => item.defaultExpanded && !item.disabled).map((item) => item.id)
  );

  const handleToggle = useCallback(
    (itemId: string) => {
      const item = items.find((i) => i.id === itemId);
      if (item?.disabled) return;

      let newExpandedIds: string[];
      const isCurrentlyExpanded = expandedIds.includes(itemId);

      if (isCurrentlyExpanded) {
        newExpandedIds = expandedIds.filter((id) => id !== itemId);
      } else {
        if (allowMultiple) {
          newExpandedIds = [...expandedIds, itemId];
        } else {
          newExpandedIds = [itemId];
        }
      }

      setExpandedIds(newExpandedIds);
      onExpandedChange?.(newExpandedIds);
    },
    [expandedIds, allowMultiple, items, onExpandedChange]
  );

  // Use role="region" only for 6 or fewer panels (APG recommendation)
  const useRegion = items.length <= 6;

  // Dynamic heading component with proper typing
  const headingTagMap = {
    2: 'h2',
    3: 'h3',
    4: 'h4',
    5: 'h5',
    6: 'h6',
  } as const;
  const HeadingTag = headingTagMap[headingLevel];

  return (
    <div className={`apg-accordion ${className}`.trim()}>
      {items.map((item) => {
        const headerId = `${instanceId}-header-${item.id}`;
        const panelId = `${instanceId}-panel-${item.id}`;
        const isExpanded = expandedIds.includes(item.id);

        const itemClass = `apg-accordion-item ${
          isExpanded ? 'apg-accordion-item--expanded' : ''
        } ${item.disabled ? 'apg-accordion-item--disabled' : ''}`.trim();

        const triggerClass = `apg-accordion-trigger ${
          isExpanded ? 'apg-accordion-trigger--expanded' : ''
        }`.trim();

        const iconClass = `apg-accordion-icon ${
          isExpanded ? 'apg-accordion-icon--expanded' : ''
        }`.trim();

        const panelClass = `apg-accordion-panel ${
          isExpanded ? 'apg-accordion-panel--expanded' : 'apg-accordion-panel--collapsed'
        }`.trim();

        return (
          <div key={item.id} className={itemClass}>
            <HeadingTag className="apg-accordion-header">
              <button
                type="button"
                id={headerId}
                aria-expanded={isExpanded}
                aria-controls={panelId}
                aria-disabled={item.disabled || undefined}
                disabled={item.disabled}
                className={triggerClass}
                onClick={() => handleToggle(item.id)}
              >
                <span className="apg-accordion-trigger-content">{item.header}</span>
                <span className={iconClass} aria-hidden="true">
                  <svg viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2">
                    <polyline points="6 9 12 15 18 9" />
                  </svg>
                </span>
              </button>
            </HeadingTag>
            <div
              role={useRegion ? 'region' : undefined}
              id={panelId}
              aria-labelledby={useRegion ? headerId : undefined}
              className={panelClass}
            >
              <div className="apg-accordion-panel-content">{item.content}</div>
            </div>
          </div>
        );
      })}
    </div>
  );
}

export default Accordion;

Usage

Example
import { Accordion } from './Accordion';

const items = [
  {
    id: 'section1',
    header: 'First Section',
    content: 'Content for the first section...',
    defaultExpanded: true,
  },
  {
    id: 'section2',
    header: 'Second Section',
    content: 'Content for the second section...',
  },
];

function App() {
  return (
    <Accordion
      items={items}
      headingLevel={3}
      allowMultiple={false}
      onExpandedChange={(ids) => console.log('Expanded:', ids)}
    />
  );
}

API

PropTypeDefaultDescription
itemsAccordionItem[]requiredArray of accordion items
allowMultiplebooleanfalseAllow multiple panels to be expanded
headingLevel2 | 3 | 4 | 5 | 63Heading level for accessibility
onExpandedChange(ids: string[]) => void-Callback when expansion changes
classNamestring""Additional CSS class

AccordionItem Props

PropTypeDefaultDescription
idstringrequiredUnique item identifier
headerstringrequiredHeader text for the accordion trigger
contentstringrequiredContent of the accordion panel
disabledbooleanfalseWhether the item is disabled
defaultExpandedbooleanfalseWhether the item is initially expanded

Testing

Tests verify APG compliance across keyboard interaction, ARIA attributes, and accessibility requirements. The Accordion component uses a two-layer testing strategy.

Testing Strategy

Unit Tests (Testing Library)

Verify the component's rendered output using framework-specific testing libraries. These tests ensure correct HTML structure and ARIA attributes.

  • ARIA attributes (aria-expanded, aria-controls, aria-labelledby)
  • Keyboard interaction (Enter, Space)
  • Expand/collapse behavior
  • Accessibility via jest-axe

E2E Tests (Playwright)

Verify component behavior in a real browser environment across all frameworks. These tests cover interactions and cross-framework consistency.

  • Click interactions
  • Enter / Space toggle
  • ARIA structure validation in live browser
  • axe-core accessibility scanning
  • Cross-framework consistency checks

Test Categories

High Priority: APG Keyboard Interaction (Unit + E2E)

TestDescription
Enter keyExpands/collapses the focused panel
Space keyExpands/collapses the focused panel

High Priority: APG ARIA Attributes (Unit + E2E)

TestDescription
aria-expandedHeader button reflects expand/collapse state
aria-controlsHeader references its panel via aria-controls
aria-labelledbyPanel references its header via aria-labelledby
role="region"Panel has region role (6 or fewer panels)
No region (7+)Panel omits region role when 7+ panels
aria-disabledDisabled items have aria-disabled="true"

High Priority: Click Interaction (Unit + E2E)

TestDescription
Click expandsClicking header expands panel
Click collapsesClicking expanded header collapses panel
Single expansionOpening panel closes other panels (default)
Multiple expansionMultiple panels can be open with allowMultiple

High Priority: Heading Structure (Unit + E2E)

TestDescription
headingLevel propUses correct heading element (h2, h3, etc.)

Medium Priority: Disabled State (Unit + E2E)

TestDescription
Disabled no clickClicking disabled header does not expand
Disabled no keyboardEnter/Space does not activate disabled header

Medium Priority: Accessibility (Unit + E2E)

TestDescription
axe violationsNo WCAG 2.1 AA violations (via jest-axe/axe-core)

Low Priority: Cross-framework Consistency (E2E)

TestDescription
All frameworks renderReact, Vue, Svelte, Astro all render accordions
Consistent ARIAAll frameworks have consistent ARIA structure

Example Test Code

The following is the actual E2E test file (e2e/accordion.spec.ts).

e2e/accordion.spec.ts
import { test, expect } from '@playwright/test';
import AxeBuilder from '@axe-core/playwright';

/**
 * E2E Tests for Accordion Pattern
 *
 * A vertically stacked set of interactive headings that each reveal
 * a section of content.
 *
 * APG Reference: https://www.w3.org/WAI/ARIA/apg/patterns/accordion/
 */

const frameworks = ['react', 'vue', 'svelte', 'astro'] as const;

// ============================================
// Helper Functions
// ============================================

const getAccordion = (page: import('@playwright/test').Page) => {
  return page.locator('.apg-accordion');
};

const getAccordionHeaders = (page: import('@playwright/test').Page) => {
  return page.locator('.apg-accordion-trigger');
};

// ============================================
// Framework-specific Tests
// ============================================

for (const framework of frameworks) {
  test.describe(`Accordion (${framework})`, () => {
    test.beforeEach(async ({ page }) => {
      await page.goto(`patterns/accordion/${framework}/demo/`);
      await getAccordion(page).first().waitFor();

      // Wait for hydration to complete - aria-controls should have a proper ID (not starting with hyphen)
      const firstHeader = getAccordionHeaders(page).first();
      await expect
        .poll(async () => {
          const id = await firstHeader.getAttribute('aria-controls');
          // ID should be non-empty and not start with hyphen (Svelte pre-hydration)
          return id && id.length > 1 && !id.startsWith('-');
        })
        .toBe(true);
    });

    // ------------------------------------------
    // 🔴 High Priority: APG ARIA Structure
    // ------------------------------------------
    test.describe('APG: ARIA Structure', () => {
      test('accordion headers have aria-expanded attribute', async ({ page }) => {
        const headers = getAccordionHeaders(page);
        const firstHeader = headers.first();

        // Should have aria-expanded (either true or false)
        const expanded = await firstHeader.getAttribute('aria-expanded');
        expect(['true', 'false']).toContain(expanded);
      });

      test('accordion headers have aria-controls referencing panel', async ({ page }) => {
        const headers = getAccordionHeaders(page);
        const firstHeader = headers.first();

        // Wait for aria-controls to be set
        await expect(firstHeader).toHaveAttribute('aria-controls', /.+/);

        const controlsId = await firstHeader.getAttribute('aria-controls');
        expect(controlsId).toBeTruthy();

        // Panel with that ID should exist
        const panel = page.locator(`[id="${controlsId}"]`);
        await expect(panel).toBeAttached();
      });

      test('panels have role="region" when 6 or fewer items', async ({ page }) => {
        const accordion = getAccordion(page).first();
        const headers = accordion.locator('.apg-accordion-trigger');
        const count = await headers.count();

        if (count <= 6) {
          const panels = accordion.locator('.apg-accordion-panel');
          const firstPanel = panels.first();
          await expect(firstPanel).toHaveRole('region');
        }
      });

      test('panels have aria-labelledby referencing header', async ({ page }) => {
        const accordion = getAccordion(page).first();
        const headers = accordion.locator('.apg-accordion-trigger');
        const count = await headers.count();

        // Only check aria-labelledby when role="region" is present (≤6 items)
        if (count <= 6) {
          const firstHeader = headers.first();

          // Wait for aria-controls to be set
          await expect(firstHeader).toHaveAttribute('aria-controls', /.+/);

          const headerId = await firstHeader.getAttribute('id');
          const controlsId = await firstHeader.getAttribute('aria-controls');
          const panel = page.locator(`[id="${controlsId}"]`);

          await expect(panel).toHaveAttribute('aria-labelledby', headerId!);
        }
      });
    });

    // ------------------------------------------
    // 🔴 High Priority: Click Interaction
    // ------------------------------------------
    test.describe('APG: Click Interaction', () => {
      test('clicking header toggles panel expansion', async ({ page }) => {
        const accordion = getAccordion(page).first();
        // Use second header which is not expanded by default
        const header = accordion.locator('.apg-accordion-trigger').nth(1);

        // Wait for component to be interactive (hydration complete)
        await expect(header).toHaveAttribute('aria-expanded', 'false');

        await header.click();

        await expect(header).toHaveAttribute('aria-expanded', 'true');
      });

      test('single expansion mode: opening one panel closes others', async ({ page }) => {
        // First accordion uses single expansion mode
        const accordion = getAccordion(page).first();
        const headers = accordion.locator('.apg-accordion-trigger');

        // Wait for hydration - first header should be expanded by default
        const firstHeader = headers.first();
        await expect(firstHeader).toHaveAttribute('aria-expanded', 'true');

        // Click second header
        const secondHeader = headers.nth(1);
        await secondHeader.click();

        // Second should be open, first should be closed
        await expect(secondHeader).toHaveAttribute('aria-expanded', 'true');
        await expect(firstHeader).toHaveAttribute('aria-expanded', 'false');
      });
    });

    // ------------------------------------------
    // 🔴 High Priority: Keyboard Interaction
    // ------------------------------------------
    test.describe('APG: Keyboard Interaction', () => {
      test('Enter/Space toggles panel expansion', async ({ page }) => {
        const accordion = getAccordion(page).first();
        // Use second header which is collapsed by default
        const header = accordion.locator('.apg-accordion-trigger').nth(1);

        // Wait for component to be ready
        await expect(header).toHaveAttribute('aria-expanded', 'false');

        // Click to set focus (this also opens the panel)
        await header.click();
        await expect(header).toBeFocused();
        await expect(header).toHaveAttribute('aria-expanded', 'true');

        // Press Enter to toggle (should collapse)
        await expect(header).toBeFocused();
        await header.press('Enter');
        await expect(header).toHaveAttribute('aria-expanded', 'false');

        // Press Space to toggle (should expand)
        await expect(header).toBeFocused();
        await header.press('Space');
        await expect(header).toHaveAttribute('aria-expanded', 'true');
      });
    });

    // ------------------------------------------
    // 🟡 Medium Priority: Disabled State
    // ------------------------------------------
    test.describe('Disabled State', () => {
      test('disabled header cannot be clicked to expand', async ({ page }) => {
        // Third accordion has disabled items
        const accordions = getAccordion(page);
        const count = await accordions.count();

        // Find accordion with disabled item
        for (let i = 0; i < count; i++) {
          const accordion = accordions.nth(i);
          const disabledHeader = accordion.locator('.apg-accordion-trigger[disabled]');

          if ((await disabledHeader.count()) > 0) {
            const header = disabledHeader.first();
            const initialExpanded = await header.getAttribute('aria-expanded');

            await header.click({ force: true });

            // State should not change
            await expect(header).toHaveAttribute('aria-expanded', initialExpanded!);
            break;
          }
        }
      });
    });

    // ------------------------------------------
    // 🟢 Low Priority: Accessibility
    // ------------------------------------------
    test.describe('Accessibility', () => {
      test('has no axe-core violations', async ({ page }) => {
        const accordion = getAccordion(page);
        await accordion.first().waitFor();

        const results = await new AxeBuilder({ page })
          .include('.apg-accordion')
          .disableRules(['color-contrast'])
          .analyze();

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

// ============================================
// Cross-framework Consistency Tests
// ============================================

test.describe('Accordion - Cross-framework Consistency', () => {
  test('all frameworks have accordions', async ({ page }) => {
    for (const framework of frameworks) {
      await page.goto(`patterns/accordion/${framework}/demo/`);
      await getAccordion(page).first().waitFor();

      const accordions = getAccordion(page);
      const count = await accordions.count();
      expect(count).toBeGreaterThan(0);
    }
  });

  test('all frameworks support click to expand', async ({ page }) => {
    for (const framework of frameworks) {
      await page.goto(`patterns/accordion/${framework}/demo/`);
      await getAccordion(page).first().waitFor();

      const accordion = getAccordion(page).first();
      // Use second header which is not expanded by default
      const header = accordion.locator('.apg-accordion-trigger').nth(1);

      // Wait for the component to be interactive (not expanded by default)
      await expect(header).toHaveAttribute('aria-expanded', 'false');

      // Click to toggle
      await header.click();

      // State should change to expanded
      await expect(header).toHaveAttribute('aria-expanded', 'true');
    }
  });

  test('all frameworks have consistent ARIA structure', async ({ page }) => {
    for (const framework of frameworks) {
      await page.goto(`patterns/accordion/${framework}/demo/`);
      await getAccordion(page).first().waitFor();

      const accordion = getAccordion(page).first();
      const header = accordion.locator('.apg-accordion-trigger').first();

      // Wait for hydration - aria-controls should be set
      await expect(header).toHaveAttribute('aria-controls', /.+/);

      // Check aria-expanded exists
      const expanded = await header.getAttribute('aria-expanded');
      expect(['true', 'false']).toContain(expanded);

      // Check aria-controls exists and references valid panel
      const controlsId = await header.getAttribute('aria-controls');
      expect(controlsId).toBeTruthy();

      const panel = page.locator(`[id="${controlsId}"]`);
      await expect(panel).toBeAttached();
    }
  });
});

Running Tests

# Run unit tests for Accordion
npm run test -- accordion

# Run E2E tests for Accordion (all frameworks)
npm run test:e2e:pattern --pattern=accordion

# Run E2E tests for specific framework
npm run test:e2e:react:pattern --pattern=accordion

npm run test:e2e:vue:pattern --pattern=accordion

npm run test:e2e:svelte:pattern --pattern=accordion

npm run test:e2e:astro:pattern --pattern=accordion

Testing Tools

See the Testing Strategy guide for details.

Accordion.test.tsx
import { render, screen } from '@testing-library/react';
import userEvent from '@testing-library/user-event';
import { axe } from 'jest-axe';
import { describe, expect, it, vi } from 'vitest';
import { Accordion, type AccordionItem } from './Accordion';

// Test accordion data
const defaultItems: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1' },
  { id: 'section2', header: 'Section 2', content: 'Content 2' },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

const itemsWithDisabled: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1' },
  { id: 'section2', header: 'Section 2', content: 'Content 2', disabled: true },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

const itemsWithDefaultExpanded: AccordionItem[] = [
  { id: 'section1', header: 'Section 1', content: 'Content 1', defaultExpanded: true },
  { id: 'section2', header: 'Section 2', content: 'Content 2' },
  { id: 'section3', header: 'Section 3', content: 'Content 3' },
];

// 7+ items (for region role test)
const manyItems: AccordionItem[] = Array.from({ length: 7 }, (_, i) => ({
  id: `section${i + 1}`,
  header: `Section ${i + 1}`,
  content: `Content ${i + 1}`,
}));

describe('Accordion', () => {
  // 🔴 High Priority: APG Core Compliance
  describe('APG: Keyboard Interaction', () => {
    it('toggles panel with Enter', async () => {
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} />);

      const button = screen.getByRole('button', { name: 'Section 1' });
      button.focus();

      expect(button).toHaveAttribute('aria-expanded', 'false');
      await user.keyboard('{Enter}');
      expect(button).toHaveAttribute('aria-expanded', 'true');
      await user.keyboard('{Enter}');
      expect(button).toHaveAttribute('aria-expanded', 'false');
    });

    it('toggles panel with Space', async () => {
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} />);

      const button = screen.getByRole('button', { name: 'Section 1' });
      button.focus();

      expect(button).toHaveAttribute('aria-expanded', 'false');
      await user.keyboard(' ');
      expect(button).toHaveAttribute('aria-expanded', 'true');
    });
  });

  describe('APG: ARIA Attributes', () => {
    it('header buttons have aria-expanded', () => {
      render(<Accordion items={defaultItems} />);
      const buttons = screen.getAllByRole('button');

      buttons.forEach((button) => {
        expect(button).toHaveAttribute('aria-expanded');
      });
    });

    it('has aria-expanded="true" on open panel', async () => {
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} />);

      const button = screen.getByRole('button', { name: 'Section 1' });
      await user.click(button);

      expect(button).toHaveAttribute('aria-expanded', 'true');
    });

    it('has aria-expanded="false" on closed panel', () => {
      render(<Accordion items={defaultItems} />);
      const button = screen.getByRole('button', { name: 'Section 1' });

      expect(button).toHaveAttribute('aria-expanded', 'false');
    });

    it('header aria-controls matches panel id', () => {
      render(<Accordion items={defaultItems} />);
      const button = screen.getByRole('button', { name: 'Section 1' });
      const ariaControls = button.getAttribute('aria-controls');

      expect(ariaControls).toBeTruthy();
      expect(document.getElementById(ariaControls!)).toBeInTheDocument();
    });

    it('panels have role="region" when 6 or fewer', () => {
      render(<Accordion items={defaultItems} />);
      const regions = screen.getAllByRole('region');

      expect(regions).toHaveLength(3);
    });

    it('panels do not have role="region" when 7 or more', () => {
      render(<Accordion items={manyItems} />);
      const regions = screen.queryAllByRole('region');

      expect(regions).toHaveLength(0);
    });

    it('panel aria-labelledby matches header id', () => {
      render(<Accordion items={defaultItems} />);
      const button = screen.getByRole('button', { name: 'Section 1' });
      const regions = screen.getAllByRole('region');

      expect(regions[0]).toHaveAttribute('aria-labelledby', button.id);
    });

    it('disabled item has aria-disabled="true"', () => {
      render(<Accordion items={itemsWithDisabled} />);
      const disabledButton = screen.getByRole('button', { name: 'Section 2' });

      expect(disabledButton).toHaveAttribute('aria-disabled', 'true');
    });
  });

  describe('APG: Heading Structure', () => {
    it('uses h3 element when headingLevel=3', () => {
      render(<Accordion items={defaultItems} headingLevel={3} />);
      const headings = document.querySelectorAll('h3');

      expect(headings).toHaveLength(3);
    });

    it('uses h2 element when headingLevel=2', () => {
      render(<Accordion items={defaultItems} headingLevel={2} />);
      const headings = document.querySelectorAll('h2');

      expect(headings).toHaveLength(3);
    });
  });

  // 🟡 Medium Priority: Accessibility Validation
  describe('Accessibility', () => {
    it('has no WCAG 2.1 AA violations', async () => {
      const { container } = render(<Accordion items={defaultItems} />);
      const results = await axe(container);
      expect(results).toHaveNoViolations();
    });
  });

  describe('Props', () => {
    it('can specify initial expanded state with defaultExpanded', () => {
      render(<Accordion items={itemsWithDefaultExpanded} />);
      const button = screen.getByRole('button', { name: 'Section 1' });

      expect(button).toHaveAttribute('aria-expanded', 'true');
    });

    it('only one panel expanded when allowMultiple=false (default)', async () => {
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} />);

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      const button2 = screen.getByRole('button', { name: 'Section 2' });

      await user.click(button1);
      expect(button1).toHaveAttribute('aria-expanded', 'true');

      await user.click(button2);
      expect(button1).toHaveAttribute('aria-expanded', 'false');
      expect(button2).toHaveAttribute('aria-expanded', 'true');
    });

    it('multiple panels can be expanded when allowMultiple=true', async () => {
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} allowMultiple />);

      const button1 = screen.getByRole('button', { name: 'Section 1' });
      const button2 = screen.getByRole('button', { name: 'Section 2' });

      await user.click(button1);
      await user.click(button2);

      expect(button1).toHaveAttribute('aria-expanded', 'true');
      expect(button2).toHaveAttribute('aria-expanded', 'true');
    });

    it('calls onExpandedChange when expanded state changes', async () => {
      const handleExpandedChange = vi.fn();
      const user = userEvent.setup();
      render(<Accordion items={defaultItems} onExpandedChange={handleExpandedChange} />);

      await user.click(screen.getByRole('button', { name: 'Section 1' }));

      expect(handleExpandedChange).toHaveBeenCalledWith(['section1']);
    });
  });

  describe('Edge Cases', () => {
    it('disabled item does not toggle on click', async () => {
      const user = userEvent.setup();
      render(<Accordion items={itemsWithDisabled} />);

      const disabledButton = screen.getByRole('button', { name: 'Section 2' });

      expect(disabledButton).toHaveAttribute('aria-expanded', 'false');
      await user.click(disabledButton);
      expect(disabledButton).toHaveAttribute('aria-expanded', 'false');
    });

    it('disabled item with defaultExpanded is not expanded', () => {
      const items: AccordionItem[] = [
        {
          id: 'section1',
          header: 'Section 1',
          content: 'Content 1',
          disabled: true,
          defaultExpanded: true,
        },
      ];
      render(<Accordion items={items} />);

      const button = screen.getByRole('button', { name: 'Section 1' });
      expect(button).toHaveAttribute('aria-expanded', 'false');
    });
  });

  // 🟢 Low Priority: Extensibility
  describe('HTML Attribute Inheritance', () => {
    it('applies className to container', () => {
      const { container } = render(<Accordion items={defaultItems} className="custom-accordion" />);
      const accordionContainer = container.firstChild as HTMLElement;
      expect(accordionContainer).toHaveClass('custom-accordion');
    });
  });
});

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