accessibility-wcag（无障碍 WCAG）

Accessibility WCAG Skill

Purpose

This skill ensures all web content meets WCAG 2.1 Level AA standards for accessibility, making websites usable by people with disabilities including visual, auditory, motor, and cognitive impairments.

Rules

WCAG 2.1 AA Requirements

WCAG is organized around four principles (POUR):

1. Perceivable - Information must be presentable in ways users can perceive
2. Operable - Interface must be operable by all users
3. Understandable - Information and operation must be understandable
4. Robust - Content must be robust enough for assistive technologies

Perceivable Requirements

Text Alternatives (1.1)

MUST:

• Provide alt text for all meaningful images
• Use empty alt="" for decorative images
• Provide captions for audio/video content
• Provide transcripts for audio-only content
• Use descriptive link text (not "click here")

Examples:

<!-- GOOD: Meaningful alt text -->
<img src="security-audit.jpg" alt="Security professional reviewing network logs on dual monitors">

<!-- GOOD: Decorative image -->
<img src="divider.png" alt="" aria-hidden="true">

<!-- BAD: Missing alt -->
<img src="chart.png">

<!-- BAD: Useless alt text -->
<img src="photo.jpg" alt="Image">

Time-based Media (1.2)

MUST:

• Provide captions for videos (prerecorded and live)
• Provide audio descriptions for video content
• Provide transcripts for audio content

Adaptable Content (1.3)

MUST:

• Use semantic HTML (headings, lists, tables correctly)
• Ensure content is accessible without CSS
• Don't rely on sensory characteristics alone (color, shape, position)
• Use proper reading order in DOM

Examples:

<!-- GOOD: Semantic markup -->
<nav aria-label="Main navigation">
  <ul>
    <li><a href="/">Home</a></li>
    <li><a href="/about">About</a></li>
  </ul>
</nav>

<!-- BAD: Div soup -->
<div class="nav">
  <div class="item"><a href="/">Home</a></div>
  <div class="item"><a href="/about">About</a></div>
</div>

Distinguishable Content (1.4)

MUST:

• Maintain color contrast ratio of at least 4.5:1 for normal text
• Maintain color contrast ratio of at least 3:1 for large text (18pt+ or 14pt+ bold)
• Don't use color alone to convey information
• Allow text resize up to 200% without loss of functionality
• Avoid background audio that can't be paused/stopped
• Ensure text can be selected and copied

Color Contrast Examples:

/* GOOD: High contrast (7:1) */
.text {
  color: #000000; /* Black */
  background-color: #FFFFFF; /* White */
}

/* GOOD: Sufficient contrast (4.6:1) */
.link {
  color: #0066CC; /* Blue */
  background-color: #FFFFFF; /* White */
}

/* BAD: Insufficient contrast (2.3:1) */
.subtle-text {
  color: #CCCCCC; /* Light gray */
  background-color: #FFFFFF; /* White */
}

Operable Requirements

Keyboard Accessible (2.1)

MUST:

• Make all functionality available via keyboard
• Provide visible focus indicators
• Don't create keyboard traps
• Ensure logical tab order
• Provide keyboard shortcuts for complex interfaces

Examples:

<!-- GOOD: Button is keyboard accessible -->
<button onclick="submitForm()">Submit</button>

<!-- BAD: Div onClick is not keyboard accessible -->
<div onclick="submitForm()">Submit</div>

<!-- BETTER: If you must use div, add role and tabindex -->
<div role="button" tabindex="0" onclick="submitForm()" onkeypress="handleKeyPress(event)">
  Submit
</div>

/* GOOD: Visible focus indicator */
a:focus,
button:focus {
  outline: 2px solid #0066CC;
  outline-offset: 2px;
}

/* BAD: Removing focus outline without replacement */
*:focus {
  outline: none; /* Never do this without providing alternative! */
}

Enough Time (2.2)

MUST:

• Allow users to turn off, adjust, or extend time limits
• Provide pause, stop, hide for auto-updating content
• No time limits unless essential (auctions, real-time games)

Seizures and Physical Reactions (2.3)

MUST NOT:

• Use content that flashes more than 3 times per second
• Create large flashing areas

Navigable (2.4)

MUST:

• Provide skip links to bypass repeated content
• Use descriptive page titles
• Ensure logical focus order
• Provide clear link purposes
• Offer multiple ways to navigate (menu, search, sitemap)
• Provide visible focus indicators
• Use clear headings and labels

Examples:

<!-- GOOD: Skip link -->
<a href="#main-content" class="skip-link">Skip to main content</a>

<nav>...</nav>

<main id="main-content">...</main>

<!-- GOOD: Descriptive title -->
<title>Security Services - ISO 27001 Implementation | Hack23</title>

<!-- BAD: Generic title -->
<title>Services</title>

Input Modalities (2.5)

MUST:

• Ensure touch targets are at least 44×44 pixels
• Don't rely on device motion alone
• Allow cancellation of pointer events
• Make clickable label text match accessible name

Understandable Requirements

Readable (3.1)

MUST:

• Specify language of page with lang attribute
• Specify language of passages that differ from page language
• Keep content at appropriate reading level (when possible)

Examples:

<!-- GOOD: Language specified -->
<html lang="en">

<!-- GOOD: Foreign language phrase -->
<p>The phrase <span lang="fr">je ne sais quoi</span> is French.</p>

Predictable (3.2)

MUST:

• Don't change context on focus
• Don't change context on input (without warning)
• Use consistent navigation across pages
• Use consistent identification of components

Input Assistance (3.3)

MUST:

• Identify input errors clearly
• Provide labels or instructions for user input
• Provide error suggestions when possible
• Prevent errors in legal/financial transactions
• Allow review/confirmation before final submission

Examples:

<!-- GOOD: Clear label and error -->
<label for="email">Email Address *</label>
<input type="email" id="email" aria-required="true" aria-describedby="email-error">
<span id="email-error" class="error" role="alert">
  Please enter a valid email address (e.g., name@example.com)
</span>

<!-- GOOD: Required field indicator -->
<label for="password">
  Password *
  <span class="required-note">(required)</span>
</label>
<input type="password" id="password" aria-required="true">

Robust Requirements

Compatible (4.1)

MUST:

• Ensure HTML is valid (no duplicate IDs, proper nesting)
• Use ARIA correctly (roles, states, properties)
• Provide name, role, value for all UI components
• Ensure status messages can be programmatically determined

ARIA Examples:

<!-- GOOD: ARIA for custom component -->
<div role="tablist" aria-label="Account settings">
  <button role="tab" aria-selected="true" aria-controls="panel-1" id="tab-1">
    Profile
  </button>
  <button role="tab" aria-selected="false" aria-controls="panel-2" id="tab-2">
    Security
  </button>
</div>
<div role="tabpanel" id="panel-1" aria-labelledby="tab-1">
  <!-- Profile content -->
</div>
<div role="tabpanel" id="panel-2" aria-labelledby="tab-2" hidden>
  <!-- Security content -->
</div>

<!-- GOOD: Status message -->
<div role="status" aria-live="polite" aria-atomic="true">
  Changes saved successfully
</div>

ARIA Best Practices

Use ARIA When:

• Native HTML element doesn't exist for your component
• Need to enhance semantic meaning
• Need to communicate state or property not available in HTML

ARIA Landmarks:

<header role="banner">
<nav role="navigation" aria-label="Main navigation">
<main role="main">
<aside role="complementary">
<footer role="contentinfo">

ARIA States and Properties:

• aria-label - Provides accessible name
• aria-labelledby - References element that labels this one
• aria-describedby - References element that describes this one
• aria-hidden - Hides element from screen readers
• aria-live - Announces dynamic content changes
• aria-expanded - Indicates if expandable element is open
• aria-pressed - Indicates toggle button state
• aria-current - Indicates current item in set

Testing Checklist

MUST TEST:

1. Keyboard Navigation

- Tab through all interactive elements - Use Enter/Space to activate buttons/links - Verify visible focus indicators - Check for keyboard traps

1. Screen Reader

- Test with NVDA (Windows), VoiceOver (Mac), or JAWS - Verify all content is announced - Check heading structure - Test form labels and error messages

1. Color Contrast

- Use WebAIM Contrast Checker - Test all text/background combinations - Check focus indicators

1. Zoom/Resize

- Zoom to 200% and verify functionality - Test with browser text-only zoom - Verify responsive design works

1. Automated Tools

- WAVE (browser extension) - axe DevTools - Lighthouse accessibility audit - Pa11y

Common Accessibility Errors

1. Missing Alt Text

<!-- BAD -->
<img src="logo.png">

<!-- GOOD -->
<img src="logo.png" alt="Hack23 Cybersecurity">

2. Poor Color Contrast

/* BAD: 2.5:1 ratio */
color: #999999;
background: #FFFFFF;

/* GOOD: 7:1 ratio */
color: #333333;
background: #FFFFFF;

3. Missing Form Labels

<!-- BAD -->
<input type="text" placeholder="Email">

<!-- GOOD -->
<label for="email">Email</label>
<input type="text" id="email">

4. Empty Links

<!-- BAD -->
<a href="report.pdf">
  <img src="pdf-icon.png">
</a>

<!-- GOOD -->
<a href="report.pdf">
  <img src="pdf-icon.png" alt="Download Annual Report (PDF, 2MB)">
</a>

5. Non-descriptive Link Text

<!-- BAD -->
<a href="/services">Click here</a> for our services.

<!-- GOOD -->
<a href="/services">View our cybersecurity services</a>

Related ISMS Policies

• Information Security Policy - Accessibility as part of service delivery

Related Documentation

• accessibility-statement.html - Published accessibility statement
• html-css-best-practices SKILL.md - Semantic HTML foundation

Resources

• WCAG 2.1: https://www.w3.org/WAI/WCAG21/quickref/
• WebAIM: https://webaim.org/
• A11Y Project: https://www.a11yproject.com/
• MDN Accessibility: https://developer.mozilla.org/en-US/docs/Web/Accessibility

Accessibility Statement

Every website MUST include an accessibility statement at /accessibility-statement.html that includes:

• Commitment to accessibility
• WCAG 2.1 AA conformance claim
• Known issues and limitations
• Contact information for accessibility concerns
• Date of last review