accessibility（无障碍）

Accessibility (WCAG 2.2)

This skill ensures that digital interfaces are Perceivable, Operable, Understandable, and Robust (POUR) for all users, including those using screen readers, switch controls, or keyboard navigation. It focuses on the technical implementation of WCAG 2.2 success criteria.

When to Use

• Defining UI component specifications for Web, iOS, or Android.
• Auditing existing code for accessibility barriers or compliance gaps.
• Implementing new WCAG 2.2 standards like Target Size (Minimum) and Focus Appearance.
• Mapping high-level design requirements to technical attributes (ARIA roles, traits, hints).

Core Concepts

• POUR Principles: The foundation of WCAG (Perceivable, Operable, Understandable, Robust).
• Semantic Mapping: Using native elements over generic containers to provide built-in accessibility.
• Accessibility Tree: The representation of the UI that assistive technologies actually "read."
• Focus Management: Controlling the order and visibility of the keyboard/screen reader cursor.
• Labeling & Hints: Providing context through aria-label, accessibilityLabel, and contentDescription.

How It Works

Step 1: Identify the Component Role

Determine the functional purpose (e.g., Is this a button, a link, or a tab?). Use the most semantic native element available before resorting to custom roles.

Step 2: Define Perceivable Attributes

• Ensure text contrast meets 4.5:1 (normal) or 3:1 (large/UI).
• Add text alternatives for non-text content (images, icons).
• Implement responsive reflow (up to 400% zoom without loss of function).

Step 3: Implement Operable Controls

• Ensure a minimum 24x24 CSS pixel target size (WCAG 2.2 SC 2.5.8).
• Verify all interactive elements are reachable via keyboard and have a visible focus indicator (SC 2.4.11).
• Provide single-pointer alternatives for dragging movements.

Step 4: Ensure Understandable Logic

• Use consistent navigation patterns.
• Provide descriptive error messages and suggestions for correction (SC 3.3.3).
• Implement "Redundant Entry" (SC 3.3.7) to prevent asking for the same data twice.

Step 5: Verify Robust Compatibility

• Use correct Name, Role, Value patterns.
• Implement aria-live or live regions for dynamic status updates.

Accessibility Architecture Diagram

flowchart TD
  UI["UI Component"] --> Platform{Platform?}
  Platform -->|Web| ARIA["WAI-ARIA + HTML5"]
  Platform -->|iOS| SwiftUI["Accessibility Traits + Labels"]
  Platform -->|Android| Compose["Semantics + ContentDesc"]

  ARIA --> AT["Assistive Technology (Screen Readers, Switches)"]
  SwiftUI --> AT
  Compose --> AT

Cross-Platform Mapping

Examples

Web: Accessible Search

<form role="search">
  <label for="search-input" class="sr-only">Search products</label>
  <input type="search" id="search-input" placeholder="Search..." />
  <button type="submit" aria-label="Submit Search">
    <svg aria-hidden="true">...</svg>
  </button>
</form>

iOS: Accessible Action Button

Button(action: deleteItem) {
    Image(systemName: "trash")
}
.accessibilityLabel("Delete item")
.accessibilityHint("Permanently removes this item from your list")
.accessibilityAddTraits(.isButton)

Android: Accessible Toggle

Switch(
    checked = isEnabled,
    onCheckedChange = { onToggle() },
    modifier = Modifier.semantics {
        contentDescription = "Enable notifications"
    }
)

Anti-Patterns to Avoid

• Div-Buttons: Using a <div> or <span> for a click event without adding a role and keyboard support.
• Color-Only Meaning: Indicating an error or status *only* with a color change (e.g., turning a border red).
• Uncontained Modal Focus: Modals that don't trap focus, allowing keyboard users to navigate background content while the modal is open. Focus must be contained *and* escapable via the Escape key or an explicit close button (WCAG SC 2.1.2).
• Redundant Alt Text: Using "Image of..." or "Picture of..." in alt text (screen readers already announce the role "Image").

Best Practices Checklist

• Interactive elements meet the 24x24px (Web) or 44x44pt (Native) target size.
• Focus indicators are clearly visible and high-contrast.
• Modals contain focus while open, and release it cleanly on close (Escape key or close button).
• Dropdowns and menus restore focus to the trigger element on close.
• Forms provide text-based error suggestions.
• All icon-only buttons have a descriptive text label.
• Content reflows properly when text is scaled.

References

• WCAG 2.2 Guidelines
• WAI-ARIA Authoring Practices
• iOS Accessibility Programming Guide
• iOS Human Interface Guidelines - Accessibility
• Android Accessibility Developer Guide

Related Skills

• frontend-patterns
• design-system
• liquid-glass-design
• swiftui-patterns