name	accessibility-standards
description	WCAG 2.1 AA compliance patterns, screen reader compatibility, keyboard navigation, and ARIA best practices. Use when implementing accessible interfaces, reviewing UI components, or auditing accessibility compliance. Covers semantic HTML, focus management, color contrast, and assistive technology testing.

Accessibility Standards

Overview

This skill provides comprehensive guidance for implementing WCAG 2.1 AA compliance across digital products. It establishes patterns for semantic markup, assistive technology compatibility, and inclusive interaction design.

Core Principles

1. POUR Framework

All accessibility work follows the four POUR principles:

Perceivable - Information must be presentable in ways users can perceive

Provide text alternatives for non-text content
Create content adaptable to different presentations
Make content distinguishable (color, contrast, audio control)

Operable - Interface components must be operable by all users

Make all functionality keyboard accessible
Provide sufficient time to read and use content
Avoid content that causes seizures or physical reactions
Help users navigate, find content, and determine location

Understandable - Information and operation must be understandable

Make text readable and understandable
Make pages appear and operate predictably
Help users avoid and correct mistakes

Robust - Content must be robust enough for diverse user agents

Maximize compatibility with current and future assistive technologies
Use valid, semantic markup
Ensure programmatic access to all functionality

2. Semantic HTML First

Semantic HTML is the foundation of accessibility. ARIA should enhance, never replace, proper markup.

Correct approach:

<button type="submit">Submit Form</button>

Incorrect approach:

<div role="button" tabindex="0" onclick="submit()">Submit Form</div>

Use native HTML elements whenever possible:

<button> for actions
<a href> for navigation
<input>, <select>, <textarea> for form controls
<nav>, <main>, <aside>, <header>, <footer> for landmarks
<h1> through <h6> for heading hierarchy

3. Progressive Enhancement

Build accessibility in layers:

Semantic HTML provides baseline accessibility
CSS enhances presentation without breaking structure
JavaScript adds interactivity while maintaining keyboard access
ARIA fills gaps for complex widgets not covered by HTML

Implementation Patterns

Document Structure

Every page requires proper document structure:

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Descriptive Page Title - Site Name</title>
</head>
<body>
  <a href="#main-content" class="skip-link">Skip to main content</a>

  <header role="banner">
    <nav aria-label="Main navigation">
      <!-- Navigation content -->
    </nav>
  </header>

  <main id="main-content" role="main">
    <h1>Page Heading</h1>
    <!-- Page content -->
  </main>

  <footer role="contentinfo">
    <!-- Footer content -->
  </footer>
</body>
</html>

Heading Hierarchy

Maintain logical heading order without skipping levels:

<h1>Main Page Title</h1>
  <h2>Section Title</h2>
    <h3>Subsection Title</h3>
    <h3>Another Subsection</h3>
  <h2>Another Section</h2>
    <h3>Subsection</h3>
      <h4>Sub-subsection</h4>

Skip Links

Provide skip links for keyboard users to bypass repetitive content:

.skip-link {
  position: absolute;
  top: -40px;
  left: 0;
  padding: 8px 16px;
  background: #000;
  color: #fff;
  z-index: 100;
}

.skip-link:focus {
  top: 0;
}

Focus Management

Visible Focus Indicators

Focus indicators must be visible and meet contrast requirements:

:focus {
  outline: 2px solid #005fcc;
  outline-offset: 2px;
}

/* Enhanced focus for better visibility */
:focus-visible {
  outline: 3px solid #005fcc;
  outline-offset: 3px;
  box-shadow: 0 0 0 6px rgba(0, 95, 204, 0.25);
}

/* Never remove focus indicators entirely */
:focus:not(:focus-visible) {
  outline: 2px solid transparent;
  box-shadow: 0 0 0 2px #005fcc;
}

Focus Trapping for Modals

function trapFocus(element) {
  const focusableElements = element.querySelectorAll(
    'button, [href], input, select, textarea, [tabindex]:not([tabindex="-1"])'
  );
  const firstFocusable = focusableElements[0];
  const lastFocusable = focusableElements[focusableElements.length - 1];

  element.addEventListener('keydown', (e) => {
    if (e.key !== 'Tab') return;

    if (e.shiftKey) {
      if (document.activeElement === firstFocusable) {
        lastFocusable.focus();
        e.preventDefault();
      }
    } else {
      if (document.activeElement === lastFocusable) {
        firstFocusable.focus();
        e.preventDefault();
      }
    }
  });
}

Keyboard Navigation

Standard Keyboard Patterns

Key	Action
Tab	Move focus to next focusable element
Shift+Tab	Move focus to previous focusable element
Enter/Space	Activate buttons and links
Arrow keys	Navigate within components (menus, tabs, radio groups)
Escape	Close modals, menus, dropdowns
Home/End	Move to first/last item in lists

Tab Order

Ensure logical tab order follows visual order:

<!-- Correct: Tab order matches visual order -->
<form>
  <label for="name">Name</label>
  <input id="name" type="text">

  <label for="email">Email</label>
  <input id="email" type="email">

  <button type="submit">Submit</button>
</form>

Never use positive tabindex values. Only use:

tabindex="0" to make non-interactive elements focusable
tabindex="-1" to make elements programmatically focusable but not in tab order

ARIA Patterns

When to Use ARIA

Use ARIA only when native HTML cannot achieve the required accessibility:

Custom widgets - Tabs, accordions, carousels, tree views
Dynamic content - Live regions for updates
Relationships - Connecting labels to complex controls
States - Expanded/collapsed, selected, pressed

ARIA Roles

Common roles for custom widgets:

<!-- Tab pattern -->
<div role="tablist" aria-label="Settings tabs">
  <button role="tab" aria-selected="true" aria-controls="panel1" id="tab1">
    General
  </button>
  <button role="tab" aria-selected="false" aria-controls="panel2" id="tab2">
    Security
  </button>
</div>
<div role="tabpanel" id="panel1" aria-labelledby="tab1">
  <!-- Panel content -->
</div>
<div role="tabpanel" id="panel2" aria-labelledby="tab2" hidden>
  <!-- Panel content -->
</div>

ARIA States and Properties

Attribute	Purpose	Example
`aria-expanded`	Indicates expandable element state	`aria-expanded="false"`
`aria-selected`	Indicates selection state	`aria-selected="true"`
`aria-pressed`	Indicates toggle button state	`aria-pressed="mixed"`
`aria-hidden`	Hides content from assistive tech	`aria-hidden="true"`
`aria-live`	Announces dynamic content	`aria-live="polite"`
`aria-describedby`	References descriptive content	`aria-describedby="hint"`
`aria-labelledby`	References labeling content	`aria-labelledby="heading"`

Live Regions

Announce dynamic content changes:

<!-- Polite: Announces when user is idle -->
<div aria-live="polite" aria-atomic="true">
  Form saved successfully
</div>

<!-- Assertive: Interrupts immediately (use sparingly) -->
<div aria-live="assertive" role="alert">
  Error: Please correct the highlighted fields
</div>

<!-- Status messages -->
<div role="status">
  Loading... 50% complete
</div>

Form Accessibility

Labels and Instructions

Every form control requires a label:

<!-- Explicit label association -->
<label for="username">Username</label>
<input type="text" id="username" name="username"
       aria-describedby="username-hint">
<span id="username-hint">Must be 3-20 characters</span>

<!-- Grouped controls with fieldset -->
<fieldset>
  <legend>Shipping Address</legend>
  <label for="street">Street</label>
  <input type="text" id="street">
  <!-- More fields -->
</fieldset>

Error Handling

Provide clear, actionable error messages:

<label for="email">Email</label>
<input type="email" id="email"
       aria-invalid="true"
       aria-describedby="email-error">
<span id="email-error" role="alert">
  Please enter a valid email address (example: user@domain.com)
</span>

Error message requirements:

Identify the field in error
Describe what went wrong
Provide guidance for correction
Use aria-invalid on the field
Announce errors via live region or role="alert"

Required Fields

<label for="name">
  Name <span aria-hidden="true">*</span>
  <span class="sr-only">(required)</span>
</label>
<input type="text" id="name" required aria-required="true">

Images and Media

Alternative Text

Provide meaningful alt text for informative images:

<!-- Informative image -->
<img src="chart.png" alt="Q3 revenue increased 15% compared to Q2">

<!-- Decorative image -->
<img src="divider.png" alt="" role="presentation">

<!-- Complex image with extended description -->
<figure>
  <img src="flowchart.png" alt="User registration process"
       aria-describedby="flowchart-desc">
  <figcaption id="flowchart-desc">
    The registration process begins with email verification,
    followed by profile creation, and ends with account activation.
  </figcaption>
</figure>

Video and Audio

<video controls>
  <source src="video.mp4" type="video/mp4">
  <track kind="captions" src="captions.vtt" srclang="en" label="English">
  <track kind="descriptions" src="descriptions.vtt" srclang="en"
         label="Audio descriptions">
</video>

Color and Contrast

Minimum Contrast Ratios

Content Type	Minimum Ratio (AA)	Enhanced Ratio (AAA)
Normal text (< 18pt)	4.5:1	7:1
Large text (>= 18pt or 14pt bold)	3:1	4.5:1
UI components and graphics	3:1	N/A

Never Rely on Color Alone

<!-- Bad: Color only indicates error -->
<input style="border-color: red">

<!-- Good: Color plus icon and text -->
<input aria-invalid="true" aria-describedby="error">
<span id="error">
  <svg aria-hidden="true"><!-- Error icon --></svg>
  Invalid email format
</span>

Motion and Animation

Respect User Preferences

/* Reduce motion for users who prefer it */
@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
  }
}

Auto-playing Content

Avoid auto-playing video or audio
Provide controls to pause, stop, or hide moving content
Limit animations to under 5 seconds or provide stop mechanism

Testing Methodology

Automated Testing

Run automated tools to catch common issues:

axe DevTools - Browser extension for page analysis
WAVE - Web accessibility evaluation tool
Lighthouse - Chrome DevTools accessibility audit
pa11y - Command-line accessibility testing

Automated testing catches approximately 30-40% of issues.

Manual Testing

Keyboard Testing

Disconnect or disable mouse
Navigate entire page using Tab/Shift+Tab
Verify all interactive elements are reachable
Verify focus indicators are visible
Test all keyboard shortcuts
Escape from all modals and menus

Screen Reader Testing

Test with multiple screen readers:

Platform	Screen Reader	Browser
Windows	NVDA (free)	Firefox, Chrome
Windows	JAWS	Chrome, Edge
macOS	VoiceOver	Safari
iOS	VoiceOver	Safari
Android	TalkBack	Chrome

Screen reader testing checklist:

All images have appropriate alt text
Headings convey page structure
Links and buttons have descriptive names
Form fields have labels
Error messages are announced
Dynamic content updates are announced
Tables have proper headers
Custom widgets announce state changes

Visual Testing

Zoom to 200% and verify no horizontal scrolling
Test with high contrast mode enabled
Disable images and verify content is still understandable
Test with browser text size increased

WCAG Audit

Perform manual audit against WCAG 2.1 AA success criteria. See checklists/wcag-checklist.md for the complete checklist.

Common Patterns

Modal Dialog

<div role="dialog" aria-modal="true" aria-labelledby="dialog-title">
  <h2 id="dialog-title">Confirm Action</h2>
  <p>Are you sure you want to proceed?</p>
  <button type="button">Cancel</button>
  <button type="button">Confirm</button>
</div>

Requirements:

Focus moves to dialog when opened
Focus is trapped within dialog
Escape key closes dialog
Focus returns to trigger element on close

Accordion

<div class="accordion">
  <h3>
    <button aria-expanded="true" aria-controls="section1">
      Section 1
    </button>
  </h3>
  <div id="section1" role="region" aria-labelledby="section1-heading">
    <!-- Content -->
  </div>
</div>

<nav aria-label="Main">
  <ul>
    <li><a href="/" aria-current="page">Home</a></li>
    <li>
      <button aria-expanded="false" aria-haspopup="true">
        Products
      </button>
      <ul>
        <li><a href="/products/a">Product A</a></li>
        <li><a href="/products/b">Product B</a></li>
      </ul>
    </li>
  </ul>
</nav>

Data Table

<table>
  <caption>Q3 Sales by Region</caption>
  <thead>
    <tr>
      <th scope="col">Region</th>
      <th scope="col">Units Sold</th>
      <th scope="col">Revenue</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th scope="row">North</th>
      <td>1,234</td>
      <td>$45,678</td>
    </tr>
  </tbody>
</table>

Install Skill

SKILL.md