accessibility（无障碍）

Accessibility (WCAG 2.2 AA)

Core Principles

• Semantic HTML elements and ARIA landmarks
• Keyboard-first navigation with visible focus states
• Skip links for main content in layouts
• Inclusive, people-first language

Semantic HTML

Use <header>, <nav aria-label="...">, <main id="main-content">, <section aria-labelledby="...">, <footer>. Always use heading hierarchy (h1 → h2 → h3).

Skip Links

<a href="#main-content" class="sr-only focus:not-sr-only focus:absolute ...">
    Skip to main content
</a>

Form Accessibility

• Label every control: <label for="email"> or aria-label for icon-only inputs
• Required fields: Use required aria-required="true" with visual * (aria-hidden="true")
• Error messages: Link via aria-describedby, set aria-invalid={hasError}
• On validation failure: Focus first invalid input
• Never disable submit just to block validation

<input id="email" aria-invalid={hasError} aria-describedby={hasError ? 'email-error' : undefined} />
{#if hasError}
    <p id="email-error" class="text-destructive">Please enter a valid email address</p>
{/if}

Keyboard Navigation

• Natural tab order follows DOM order — avoid positive tabindex
• Use tabindex="-1" for hidden/inactive elements
• Dialogs: Focus first interactive element on open, return focus to trigger on close
• Interactive non-button elements must handle Enter and Space key events

Icon Buttons

Always add aria-label and hide the icon from assistive technology:

<button aria-label="Delete event">
    <TrashIcon aria-hidden="true" />
</button>

When icons accompany visible text, just hide the icon: <PlusIcon aria-hidden="true" />.

ARIA Patterns

Live regions for dynamic updates:

<div aria-live="polite" aria-atomic="true">{#if loading}Loading events...{/if}</div>
<div role="alert">Error: Failed to save changes</div>

Expandable content: Use aria-expanded and aria-controls on the trigger, hidden on the panel.

Color and Contrast

• Minimum contrast ratio: 4.5:1 for normal text, 3:1 for large text and UI components
• Don't rely on color alone — combine with icons or text

<!-- ✅ Good: Icon + color + text -->
<span class="text-destructive"><AlertIcon aria-hidden="true" /> Error: Invalid input</span>

Testing

Use axe-playwright in E2E tests (AxeBuilder({page}).analyze()) to catch accessibility violations.