Accessibility Standards Knowledge Base

Reference guide for WCAG 2.1 AA requirements, ARIA, keyboard navigation, screen reader support, and accessible component patterns. Use this knowledge when auditing accessibility, scaffolding components, or reviewing frontend code.

---

WCAG 2.1 AA Requirements

WCAG is organized into 4 principles (POUR): Perceivable, Operable, Understandable, Robust.

Perceivable

Users must be able to perceive the information presented.

Criterion	ID	Requirement
Non-text Content	1.1.1	All non-text content has a text alternative (alt text, labels, captions)
Captions (Prerecorded)	1.2.2	Prerecorded audio in video has captions
Audio Description	1.2.5	Prerecorded video has audio description
Info and Relationships	1.3.1	Information and structure are programmatically determinable (semantic HTML, ARIA)
Meaningful Sequence	1.3.2	Reading/navigation order is logical and intuitive
Sensory Characteristics	1.3.3	Instructions don't rely solely on shape, size, position, or sound
Orientation	1.3.4	Content doesn't restrict to a single display orientation
Input Purpose	1.3.5	Input fields that collect user info have programmatic purpose (autocomplete)
Use of Color	1.4.1	Color is not the only visual means of conveying information
Contrast (Minimum)	1.4.3	Text has ≥4.5:1 contrast (normal) or ≥3:1 (large: 18px+ or 14px+ bold)
Resize Text	1.4.4	Text can resize up to 200% without loss of content or function
Images of Text	1.4.5	Use real text instead of images of text (exceptions: logos)
Reflow	1.4.10	Content reflows at 320px width / 256px height without horizontal scroll
Non-text Contrast	1.4.11	UI components and graphics have ≥3:1 contrast against adjacent colors
Text Spacing	1.4.12	Content adapts to: line-height 1.5x, paragraph spacing 2x, letter spacing 0.12em, word spacing 0.16em
Content on Hover/Focus	1.4.13	Hover/focus-triggered content is dismissible, hoverable, and persistent

Operable

Users must be able to operate the interface.

Criterion	ID	Requirement
Keyboard	2.1.1	All functionality is available from a keyboard
No Keyboard Trap	2.1.2	Keyboard focus can always be moved away from any component
Character Key Shortcuts	2.1.4	Single-character key shortcuts can be turned off or remapped
Timing Adjustable	2.2.1	Time limits can be extended or turned off
Pause, Stop, Hide	2.2.2	Auto-moving/updating content can be paused, stopped, or hidden
Three Flashes	2.3.1	Content doesn't flash more than 3 times per second
Skip Navigation	2.4.1	Skip-to-content link is available to bypass repeated blocks
Page Titled	2.4.2	Pages have descriptive titles
Focus Order	2.4.3	Focus order preserves meaning and operability
Link Purpose	2.4.4	Link purpose is determinable from link text (or context)
Multiple Ways	2.4.5	Multiple ways to locate content (nav, search, sitemap)
Headings and Labels	2.4.6	Headings and labels describe the topic or purpose
Focus Visible	2.4.7	Keyboard focus indicator is visible
Pointer Gestures	2.5.1	Multi-point/path gestures have single-pointer alternatives
Pointer Cancellation	2.5.2	Actions triggered on up-event, not down-event (allows cancellation)
Label in Name	2.5.3	Accessible name contains the visible label text
Motion Actuation	2.5.4	Device motion actions have UI alternatives and can be disabled

Understandable

Users must be able to understand the information and operation.

Criterion	ID	Requirement
Language of Page	3.1.1	Default language is programmatically set (lang attribute)
Language of Parts	3.1.2	Language changes within content are marked
On Focus	3.2.1	Focus doesn't trigger context changes
On Input	3.2.2	Input doesn't trigger unexpected context changes
Consistent Navigation	3.2.3	Navigation mechanisms are consistent across pages
Consistent Identification	3.2.4	Components with the same function are identified consistently
Error Identification	3.3.1	Errors are identified and described in text
Labels or Instructions	3.3.2	Labels or instructions are provided for user input
Error Suggestion	3.3.3	Error messages suggest corrections when possible
Error Prevention	3.3.4	Submissions involving legal/financial/data are reversible, verified, or confirmed

Robust

Content must be robust enough for assistive technologies.

Criterion	ID	Requirement
Parsing	4.1.1	HTML is well-formed (unique IDs, proper nesting)
Name, Role, Value	4.1.2	All UI components have accessible name, role, and state
Status Messages	4.1.3	Status messages are programmatically announced without focus change

---

ARIA Roles, States, and Properties

When to Use ARIA

First rule of ARIA: Don't use ARIA if you can use a native HTML element.

<!-- BAD: ARIA button -->
<div role="button" tabindex="0" onclick="submit()">Submit</div>

<!-- GOOD: Native button -->
<button onclick="submit()">Submit</button>

Native HTML elements have built-in keyboard handling, roles, and states. ARIA is for when no native element exists (custom widgets).

Common Roles

Role	Use Case	Native Equivalent
button	Clickable trigger	<button>
link	Navigation	<a href>
checkbox	Toggle option	<input type="checkbox">
radio	Exclusive option	<input type="radio">
tab, tablist, tabpanel	Tab interface	None
dialog	Modal/dialog	<dialog>
alert	Important message	None
status	Status update	None
menu, menuitem	Action menu	None
tree, treeitem	Tree view	None
grid, row, gridcell	Data grid	<table>
region	Generic landmark	<section> with label
navigation	Nav landmark	<nav>
banner	Page header	<header> (top-level)
main	Main content	<main>
contentinfo	Page footer	<footer> (top-level)
complementary	Supporting content	<aside>
search	Search area	<search> (HTML5.2+)

Common States and Properties

Attribute	Purpose	Values
aria-label	Accessible name (no visible label)	String
aria-labelledby	Accessible name (references visible element)	ID(s)
aria-describedby	Additional description	ID(s)
aria-expanded	Disclosure state	true / false
aria-pressed	Toggle button state	true / false / mixed
aria-checked	Checkbox/radio state	true / false / mixed
aria-selected	Selection state (tabs, options)	true / false
aria-hidden	Hidden from assistive tech	true / false
aria-disabled	Disabled state	true / false
aria-required	Required field	true / false
aria-invalid	Validation state	true / false / grammar / spelling
aria-errormessage	Error message reference	ID
aria-live	Live region update behavior	polite / assertive / off
aria-busy	Content being updated	true / false
aria-current	Current item indicator	page / step / location / date / true
aria-haspopup	Element opens a popup	true / menu / listbox / tree / grid / dialog
aria-controls	Element controls another	ID
aria-owns	Parent-child relationship override	ID(s)
aria-modal	Marks a dialog as modal	true
aria-roledescription	Custom role description	String

---

Keyboard Navigation Patterns

Focus Management

Pattern	Implementation
Tab: Move to next focusable element	Native browser behavior — ensure tabindex is correct
Shift+Tab: Move to previous	Native — same as above
Enter/Space: Activate	Buttons handle both natively. Custom elements: handle keydown
Escape: Close/dismiss	Handle in modal, dropdown, popover, tooltip handlers
Arrow keys: Navigate within widget	Tabs, menus, radio groups, grids, trees
Home/End: First/last item	Lists, menus, tabs, sliders

Roving tabindex

For composite widgets (tabs, menus, radio groups), use roving tabindex:

// Only the active item is in the tab order
items.map((item, i) => (
  <button
    key={item.id}
    role="tab"
    tabIndex={i === activeIndex ? 0 : -1}
    aria-selected={i === activeIndex}
    onKeyDown={(e) => {
      if (e.key === 'ArrowRight') setActiveIndex((activeIndex + 1) % items.length);
      if (e.key === 'ArrowLeft') setActiveIndex((activeIndex - 1 + items.length) % items.length);
      if (e.key === 'Home') setActiveIndex(0);
      if (e.key === 'End') setActiveIndex(items.length - 1);
    }}
  >
    {item.label}
  </button>
));

Focus Trapping (Modals)

function useFocusTrap(containerRef: RefObject<HTMLElement>) {
  useEffect(() => {
    const container = containerRef.current;
    if (!container) return;

    const focusableSelector = 'a[href], button:not([disabled]), input:not([disabled]), select:not([disabled]), textarea:not([disabled]), [tabindex]:not([tabindex="-1"])';

    function handleKeyDown(e: KeyboardEvent) {
      if (e.key !== 'Tab') return;

      const focusable = container.querySelectorAll<HTMLElement>(focusableSelector);
      const first = focusable[0];
      const last = focusable[focusable.length - 1];

      if (e.shiftKey && document.activeElement === first) {
        e.preventDefault();
        last.focus();
      } else if (!e.shiftKey && document.activeElement === last) {
        e.preventDefault();
        first.focus();
      }
    }

    container.addEventListener('keydown', handleKeyDown);
    return () => container.removeEventListener('keydown', handleKeyDown);
  }, [containerRef]);
}

---

Screen Reader Support

How Screen Readers Work

Screen readers traverse the accessibility tree (derived from the DOM). They announce:

1. Role: "button", "link", "heading level 2"
2. Name: The accessible name (text content, aria-label, alt, <label>)
3. State: "expanded", "checked", "disabled", "selected"
4. Description: Additional info from aria-describedby

Accessible Name Computation (priority order)

1. aria-labelledby (references another element's text)
2. aria-label (direct string)
3. Native label association (<label for>, <caption>, <legend>, <figcaption>)
4. Text content (for <button>, <a>, heading elements)
5. title attribute (last resort — unreliable across browsers)
6. placeholder (not a label — don't rely on it)

Live Regions

Announce dynamic content updates without moving focus.

<!-- Polite: announces when user is idle (default for most updates) -->
<div aria-live="polite">3 items in cart</div>

<!-- Assertive: announces immediately, interrupting current speech -->
<div role="alert">Error: Payment failed. Please try again.</div>

<!-- Status: implicit aria-live="polite" -->
<div role="status">Search returned 42 results</div>

Guidelines:

• The live region element must exist in the DOM BEFORE the content changes
• Don't create and immediately populate a live region — the screen reader won't detect the change
• Use aria-live="polite" for most updates (cart count, search results, saved confirmation)
• Use role="alert" or aria-live="assertive" only for urgent messages (errors, warnings)
• Use aria-atomic="true" when the entire region should be re-read on any change

---

Color Contrast

Requirements

Content Type	Minimum Ratio	WCAG Criterion
Normal text (< 18px or < 14px bold)	4.5:1	1.4.3 AA
Large text (≥ 18px or ≥ 14px bold)	3:1	1.4.3 AA
UI components (borders, icons)	3:1	1.4.11 AA
Focus indicators	3:1	1.4.11 AA
Disabled elements	No requirement	—
Decorative elements	No requirement	—

Checking Contrast

Tools for contrast checking:

• Browser DevTools (Chrome, Firefox) show contrast ratios in the color picker
• axe-core / axe DevTools browser extension
• WebAIM Contrast Checker
• Stark (Figma plugin)

Common Pitfalls

• Light gray text on white — #999 on #fff = 2.85:1 (FAILS). Use #767676 for 4.5:1.
• Placeholder text — Browsers default to light gray. If placeholder conveys information, ensure contrast.
• Blue links on dark backgrounds — Default blue #0000ee on #333 = 3.36:1 (fails for normal text).
• Error red — #ff0000 on white = 4:1 (fails). Use #c00 or #d32f2f for better contrast.
• Focus outline on varied backgrounds — Use double-ring technique: dark outer + light inner outline.

---

Form Accessibility

Required Pattern

<div>
  <label for="email">
    Email address
    <span aria-hidden="true">*</span>
  </label>
  <input
    id="email"
    type="email"
    required
    aria-required="true"
    autocomplete="email"
    aria-describedby="email-hint"
  />
  <p id="email-hint">We'll never share your email.</p>
</div>

Error Pattern

<div>
  <label for="password">Password</label>
  <input
    id="password"
    type="password"
    aria-invalid="true"
    aria-errormessage="password-error"
    aria-describedby="password-requirements"
  />
  <p id="password-requirements">Must be at least 8 characters.</p>
  <p id="password-error" role="alert">
    Password is too short. Please enter at least 8 characters.
  </p>
</div>

Fieldset and Legend (for groups)

<fieldset>
  <legend>Shipping method</legend>
  <label>
    <input type="radio" name="shipping" value="standard" />
    Standard (5-7 days)
  </label>
  <label>
    <input type="radio" name="shipping" value="express" />
    Express (1-2 days)
  </label>
</fieldset>

---

Accessible Component Patterns

Modal / Dialog

<dialog
  ref={dialogRef}
  aria-labelledby="dialog-title"
  aria-describedby="dialog-description"
  aria-modal="true"
>
  <h2 id="dialog-title">Confirm deletion</h2>
  <p id="dialog-description">This action cannot be undone.</p>
  <button onClick={onConfirm}>Delete</button>
  <button onClick={onClose}>Cancel</button>
</dialog>

Requirements:

• Focus moves to dialog (or first focusable element inside) on open
• Focus is trapped within the dialog while open
• Escape key closes the dialog
• Focus returns to the trigger element on close
• Background content is inert (inert attribute or aria-hidden)

Tabs

<div role="tablist" aria-label="Settings sections">
  <button role="tab" aria-selected="true" aria-controls="panel-general" id="tab-general">
    General
  </button>
  <button role="tab" aria-selected="false" aria-controls="panel-security" id="tab-security" tabIndex={-1}>
    Security
  </button>
</div>
<div role="tabpanel" id="panel-general" aria-labelledby="tab-general">
  General settings content
</div>
<div role="tabpanel" id="panel-security" aria-labelledby="tab-security" hidden>
  Security settings content
</div>

Requirements:

• Arrow keys navigate between tabs (roving tabindex)
• Tab content is only shown for the selected tab
• Tab panels are labeled by their tab

Accordion / Disclosure

<div>
  <h3>
    <button
      aria-expanded={isOpen}
      aria-controls="section-1-content"
    >
      Section 1
    </button>
  </h3>
  <div id="section-1-content" role="region" aria-labelledby="section-1-heading" hidden={!isOpen}>
    Section content
  </div>
</div>

Tooltip

<button aria-describedby="tooltip-1">
  Settings
</button>
<div id="tooltip-1" role="tooltip" hidden={!showTooltip}>
  Manage your account settings
</div>

Requirements:

• Tooltip appears on hover AND focus
• Tooltip is dismissible with Escape
• Tooltip content is hoverable (user can move mouse over tooltip)
• Tooltip persists while trigger has focus

Combobox / Autocomplete

<div>
  <label for="search">Search users</label>
  <input
    id="search"
    role="combobox"
    aria-expanded={isOpen}
    aria-controls="search-listbox"
    aria-activedescendant={activeOptionId}
    aria-autocomplete="list"
  />
  <ul id="search-listbox" role="listbox" aria-label="Search results">
    {results.map(result => (
      <li
        key={result.id}
        id={`option-${result.id}`}
        role="option"
        aria-selected={result.id === activeId}
      >
        {result.name}
      </li>
    ))}
  </ul>
</div>

Requirements:

• Arrow keys navigate options
• Enter selects the active option
• Escape closes the listbox
• Screen reader announces the active option via aria-activedescendant
• Number of results is announced (via live region or aria-live)

---

Testing Accessibility

Automated Testing

• axe-core: Run in unit tests with jest-axe or vitest-axe
• eslint-plugin-jsx-a11y: Catch common issues at lint time
• Lighthouse: Audit pages in CI
• Pa11y: Command-line accessibility testing

import { axe, toHaveNoViolations } from 'jest-axe';

expect.extend(toHaveNoViolations);

it('has no accessibility violations', async () => {
  const { container } = render(<MyComponent />);
  const results = await axe(container);
  expect(results).toHaveNoViolations();
});

Manual Testing Checklist

1. Tab through the entire page — can you reach and operate everything?
2. Use screen reader (VoiceOver on Mac, NVDA on Windows) — is everything announced?
3. Zoom to 200% — does the layout still work?
4. Set text spacing overrides — does content still fit?
5. Turn off CSS — is the content order logical?
6. Check with high contrast mode — is everything visible?
7. Test with keyboard only — no mouse/trackpad

Automated tests catch ~30% of accessibility issues. Manual testing is required for full compliance.