wcag-accessibility（WCAG 无障碍）

WCAG Accessibility (EN 301 549 / European Standard)

The Standard

The European Accessibility Act (EAA) requires digital products and services in the EU to meet EN 301 549, which references WCAG 2.2 Level AA as the technical baseline. This is not optional — it is a legal requirement for products operating in the EU market.

Default: always build to WCAG 2.2 AA. Deviating requires explicit, documented justification. Do not skip accessibility requirements because of timeline pressure or design preference.

WCAG 2.2 AA organises requirements under four principles: Perceivable, Operable, Understandable, Robust.

Perceivable

Users must be able to perceive all content and UI components.

Colour Contrast

Disabled elements are exempt. WCAG explicitly excludes inactive UI components from contrast requirements (WCAG 1.4.3 exception). A disabled button may use low-contrast text — this is intentional and correct, as it communicates the unavailable state.

Do not use colour as the only means of conveying information (e.g. a red border alone to indicate an error — add an icon or text label).

Text Alternatives

• Every meaningful image needs alt text describing its content or function
• Decorative images use alt="" so screen readers skip them
• Icons used as buttons need an accessible label: aria-label or visually hidden text
• Charts and data visualisations need a text summary or data table alternative

Captions and Transcripts

• Video content needs captions
• Audio-only content needs a transcript

Operable

Users must be able to operate all UI components.

Keyboard Navigation

All interactive elements must be reachable and operable by keyboard alone.

• Every button, link, input, and control must receive focus via Tab
• Focus order must follow the visual reading order of the page
• No keyboard traps — users must be able to navigate away from any component
• Modal dialogs must trap focus inside while open, and return focus to the trigger element on close

Focus Visibility

A visible focus indicator is required on every interactive element (WCAG 2.2 strengthens focus visibility requirements).

/* Minimum: do not remove focus outline without a replacement */
:focus-visible {
  outline: 2px solid var(--color-focus);
  outline-offset: 2px;
}

Never use outline: none without providing a custom focus style. The focus ring is not a design problem to eliminate — it is a navigation tool.

Touch Target Size

Interactive elements on touch devices must be at least 24×24px (WCAG 2.2) — 44×44px is the recommended comfortable minimum (Apple HIG, Material Design). Small icon buttons need padding to reach this size even if the visual icon is smaller.

No Seizure Triggers

Nothing on screen should flash more than 3 times per second.

Skip Links

Pages with repeated navigation must provide a "Skip to main content" link as the first focusable element, so keyboard users can bypass navigation on every page.

Understandable

Users must be able to understand the content and how the UI works.

Language

• Set lang attribute on the <html> element: <html lang="fi"> or <html lang="en">
• Mark inline content in a different language with lang on that element

Labels and Instructions

• Every form input must have a visible label — not just a placeholder (placeholders disappear on input)
• Required fields must be indicated — do not rely on colour alone; add an asterisk and a legend
• Error messages must be associated with their input via aria-describedby

Predictability

• Components that look the same must behave the same (see Consistency and Standards)
• Navigation must appear in the same location across pages
• Opening a new tab or window must be communicated in advance

Error Identification

• Form validation errors must identify which field failed
• Errors must be described in text — not only by colour or icon

Robust

Content must be interpreted reliably by assistive technologies.

Semantic HTML

Use the correct HTML element for the job. Semantics convey role, state, and structure to screen readers for free.

<!-- Correct -->
<button>Save</button>
<nav aria-label="Main navigation">...</nav>
<h1>Page title</h1>

<!-- Wrong — requires manual ARIA to replicate what the element provides natively -->
<div onclick="save()">Save</div>
<div class="nav">...</div>
<div class="heading">Page title</div>

ARIA — Use Sparingly

ARIA supplements HTML semantics where native elements fall short. It does not fix broken HTML.

Rule: no ARIA is better than incorrect ARIA. Incorrect ARIA actively breaks screen reader output.

Required patterns:

• aria-label or aria-labelledby for components with no visible text label
• aria-expanded on toggles, accordions, and dropdowns
• aria-live regions for dynamic content updates (toast notifications, search results)
• role="dialog" with aria-modal="true" on modal overlays
• aria-current="page" on the active navigation item

Status Messages

Dynamic updates (success toasts, loading states, error counts) must be announced to screen readers via aria-live or role="status" — they will not be announced automatically unless the focused element changes.

The Disabled Element Exception

WCAG 1.4.3 explicitly states: *"Text or images of text that are part of an inactive user interface component… have no contrast requirement."*

This means:

• Disabled buttons, inputs, and links may use low-contrast text and colours
• The visual dimming of disabled states is both correct and compliant
• Do not add artificial contrast to disabled elements — the reduced contrast communicates "this is unavailable"

Review Checklist