accessibility-a11y（无障碍 a11y）

Accessibility (a11y) Best Practices

You are an expert in web accessibility and inclusive design. Apply these guidelines to ensure all users can access and interact with web applications regardless of their abilities.

Core Accessibility Principles

• Follow WCAG (Web Content Accessibility Guidelines) standards
• Use semantic HTML to improve accessibility and screen reader compatibility
• Ensure high accessibility standards using ARIA roles and native accessibility props
• Design for all users including those with visual, auditory, motor, and cognitive disabilities
• Test with various assistive technologies

Semantic HTML

Structural Elements

• Use semantic elements like <header>, <main>, <footer>, <nav>, <article>, <section>, <aside>
• Employ <button> for interactive elements, not <div> or <span>
• Use proper heading hierarchy (h1-h6) without skipping levels
• Use landmarks (e.g., <nav>, <main>, <aside>) for screen reader navigation
• Avoid deprecated markup

Form Accessibility

• Associate labels with form inputs using for and id attributes
• Group related form elements with <fieldset> and <legend>
• Provide clear error messages and validation feedback
• Use appropriate input types (email, tel, number, etc.)
• Include placeholder text as supplementary hints, not replacements for labels

ARIA Implementation

When to Use ARIA

• Use ARIA roles and attributes to enhance accessibility where semantic HTML is insufficient
• Prefer native HTML elements over ARIA when possible
• Use aria-label for elements without visible text labels
• Implement aria-describedby for additional context
• Use aria-live regions for dynamic content updates

Common ARIA Patterns

• Use role="button" only when a non-button element must act as a button
• Implement aria-expanded for collapsible content
• Use aria-hidden="true" for decorative elements
• Apply aria-current="page" for navigation highlighting
• Use aria-labelledby to reference visible labels

Visual Accessibility

Color and Contrast

• Ensure sufficient color contrast for text (minimum 4.5:1 for normal text, 3:1 for large text)
• Never use color as the only means of conveying information
• Provide alternative indicators (icons, patterns, text) alongside color
• Test designs with color blindness simulators

Focus Management

• Use focus styles to indicate focus state clearly
• Ensure visible focus indicators on all interactive elements
• Manage focus appropriately when content changes dynamically
• Avoid removing outline styles without providing alternatives
• Implement logical tab order

Keyboard Navigation

Navigation Requirements

• Provide keyboard navigation for all interactive elements
• Ensure all functionality is accessible via keyboard alone
• Use tabindex appropriately (0 for natural order, -1 for programmatic focus)
• Implement keyboard shortcuts for complex interactions
• Avoid keyboard traps

Interactive Elements

• Ensure interactive elements are large enough for touch (minimum 44x44 pixels)
• Implement keyboard event handlers (onKeyDown, onKeyPress) alongside click handlers
• Support Enter and Space keys for activating buttons
• Implement arrow key navigation for complex widgets

Content Accessibility

Images and Media

• Ensure all images have descriptive alt text
• Use empty alt="" for decorative images
• Provide captions for videos
• Include transcripts for audio content
• Use descriptive link text (avoid "click here")

Text and Typography

• Use relative units (rem, em) for typography
• Ensure text can be resized up to 200% without loss of functionality
• Maintain adequate line height and letter spacing
• Avoid justified text which can create uneven spacing
• Support user preferences for reduced motion

Responsive and Adaptive Design

Mobile-First Approach

• Design mobile-first, then scale upward
• Implement responsive layouts that work across devices
• Ensure touch targets are appropriately sized
• Support both portrait and landscape orientations

User Preferences

• Respect prefers-reduced-motion for animations
• Support prefers-color-scheme for dark/light modes
• Consider prefers-contrast for high contrast needs
• Implement prefers-reduced-transparency when applicable

Testing and Validation

Automated Testing

• Use tools like Lighthouse for accessibility audits
• Integrate axe-core for automated accessibility testing
• Run accessibility checks in CI/CD pipelines
• Address all critical and serious accessibility issues

Manual Testing

• Test with screen readers (NVDA, JAWS, VoiceOver)
• Navigate entirely by keyboard
• Test with browser zoom at 200%
• Use browser accessibility inspection tools
• Test with actual users who have disabilities when possible

CSS Best Practices for Accessibility

• Use external stylesheets; avoid inline styles for maintainability
• Leverage Flexbox and Grid for robust layouts
• Use class selectors for styling (BEM naming methodology recommended)
• Implement responsive design with media queries
• Ensure hover states also have focus equivalents