accessibility

name	accessibility
description	WCAG conformance, BFSG compliance, semantic HTML, ARIA, keyboard navigation, contrast, forms, and assistive technologies. Defines binding rules for accessible web interfaces per WCAG 2.1 AA.

Accessibility

Accessible web interfaces are mandatory -- legally, ethically, and commercially.

Scope

Use this skill when: You are auditing HTML structure and semantics, setting ARIA attributes, implementing keyboard navigation, checking contrasts, designing accessible forms, making media accessible, ensuring BFSG compliance, or auditing existing interfaces for accessibility.

Principles

1. Accessibility Is a Baseline Requirement -- Not a Special Feature

Accessible design benefits EVERYONE. Situational limitations (sunlight, noisy environments, one hand occupied) affect everyone.

2. From the Start -- Not Retrofitted

Retrofitting is 10x more expensive and 10x worse. Accessibility belongs in every phase: concept, design, development, testing.

3. The Four POUR Principles Are Mandatory

Perceivable, Operable, Understandable, Robust.

4. Technology and Design Must Work Together

Not just a developer concern (HTML) and not just a design concern (contrast). Both disciplines in sync.

5. Legal Obligation (BFSG Effective June 28, 2025)

The German Accessibility Reinforcement Act (BFSG) requires many companies to provide digital accessibility. It is not optional.

Rules

Semantic HTML

• DO: Use native elements for their purpose: <button> for actions, <a> for navigation, <nav>, <main>, <article>.
• DO: Maintain a logical heading hierarchy: exactly one <h1> per page. Do not skip levels.
• DO: Use landmark elements: <header>, <nav>, <main>, <aside>, <footer>.
• DON'T: Use <div> or <span> for interactive elements. <div onclick> is NOT a button.
• DON'T: Misuse headings for styling.

ARIA Attributes

• DO: Use ARIA only when no native HTML element fulfills the purpose.
• DO: Add aria-label to interactive elements without visible text (icon buttons).
• DO: Use aria-live="polite" for dynamic content (toast notifications).
• DO: Use role="alert" for error messages.
• DON'T: Overload elements with ARIA. Redundant ARIA does harm.
• DON'T: Set aria-hidden="true" on visible, interactive elements.

Keyboard Navigation

• DO: Make ALL interactive elements reachable via keyboard (Tab, Enter, Space, Escape, Arrow keys).
• DO: Provide a visible focus indicator: min. 3:1 contrast, 2-3px outline.
• DO: Implement focus trap in modals.
• DO: Include a skip-to-content link as the first focusable element.
• DO: Ensure tab order matches the visual reading order. Use tabindex only with values 0 or -1.
• DON'T: Use tabindex > 0 (breaks natural order).
• DON'T: Set outline: none without an adequate replacement.

Contrast & Colors

• DO: Normal text: min. 4.5:1 (WCAG AA).
• DO: Large text (>= 24px / >= 18.66px bold): min. 3:1.
• DO: UI components: min. 3:1.
• DO: NEVER use color as the only signal. Always provide a second signal: text, icon, pattern.
• DO: Test for color vision deficiency (Chrome DevTools > Rendering > Emulate vision deficiencies).
• DON'T: Rely on red-green distinctions for critical information (8% of male users affected).

Images & Media

• DO: Informative images: descriptive alt text (content, not appearance).
• DO: Decorative images: alt="" (empty alt text).
• DO: Videos with captions. Audio with transcripts.
• DO: Make animations pausable. Respect prefers-reduced-motion in CSS.
• DON'T: Use flashing content (> 3 flashes/second can trigger seizures).

Forms

• DO: Associate every field with a visible <label> via for/id.
• DO: Required fields: text + aria-required="true".
• DO: Error messages directly at the field + aria-describedby.
• DO: Use autocomplete attributes on standard fields.
• DON'T: Use placeholder as a label replacement.
• DON'T: Use CAPTCHAs without an accessible alternative.

Responsive & Touch

• DO: Touch targets min. 44x44px (WCAG), preferably 48x48px.
• DO: Spacing between targets min. 8px.
• DO: Support zoom up to 200% without loss of functionality.
• DON'T: Block zooming (user-scalable=no, maximum-scale=1).

Motion & Animation

• DO: Respect prefers-reduced-motion. Reduce or remove animations.
• DO: Make automatic motion (carousels, videos) pausable.
• DON'T: Use parallax or large motion effects without a prefers-reduced-motion fallback.

Detailed pattern descriptions and code examples: see references/patterns.md

Patterns

Skip Navigation

First focusable link: "Skip to content." Visually hidden, visible on focus. Links to <main>.

Accessible Modal

role="dialog" + aria-modal="true" + aria-labelledby. Focus trap. Escape closes. Focus returns to the trigger.

Error Summary

Error summary at the top of the form with links to affected fields. role="alert". Additionally inline errors.

Accessible Accordion

<button> as trigger with aria-expanded. Content with aria-labelledby. Arrow keys for navigation.

Anti-Patterns

Div Soup

Everything built from <div> and <span>. Solution: Use native HTML elements.

Invisible Focus Indicator

outline: none without replacement. Solution: Visible focus styles with min. 3:1 contrast.

Placeholder as Label

Fields without <label>. Solution: Always use a visible label. Placeholder only as supplementary.

Auto-Playing Media

Autoplay with sound. Solution: Start only on user action. Autoplay only muted with pause option.

ARIA Overload

role="button" on a <button>. Solution: Prefer native HTML. ARIA only as a last resort.

Zoom Blocking

maximum-scale=1 in the viewport meta tag. Solution: Viewport without zoom restrictions.

Checklist

Structure & Semantics

• Exactly one <h1> per page?
• Heading hierarchy without gaps?
• Landmark elements present?
• Skip-to-content link present?
• No interactive <div> / <span> elements?

Contrast & Colors

• Normal text min. 4.5:1?
• Large text min. 3:1?
• UI components min. 3:1?
• Color never used as the only signal?
• Color vision deficiency tested?

Keyboard & Interaction

• Everything reachable via keyboard?
• Visible focus indicator?
• Focus trap in modals?
• Tab order = visual order?
• No tabindex > 0?

Images & Media

• Informative images with alt text?
• Decorative images with alt=""?
• Videos with captions?
• prefers-reduced-motion respected?

Forms

• Every field with a visible <label>?
• Required fields marked + aria-required?
• Inline errors with aria-describedby?
• No placeholder as label?

Mobile & Responsive

• Touch targets min. 44x44px?
• Zoom up to 200% possible?

Legal

• BFSG relevance assessed?
• WCAG 2.1 AA as the minimum standard?
• Accessibility statement present?

Cross-References

• ui-design -- Accessible UI components and states
• web-typography -- Readable font sizes and contrast requirements
• color-theory -- WCAG contrast requirements, color vision deficiency
• usability -- Overlap between accessibility and usability
• responsive-design -- Touch targets, zoom, mobile screen readers
• navigation-design -- Keyboard navigation, skip links, landmarks