2nd/10_Wiki/Topics/AI_and_ML/웹 접근성 및 성능 최적화.md

---
id: wiki-2026-0508-웹-접근성-및-성능-최적화
title: 웹 접근성 및 성능 최적화
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Web Accessibility, A11y, Performance Optimization, WCAG, Core Web Vitals]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [accessibility, a11y, performance, wcag, core-web-vitals, frontend]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript
  framework: React/Web
---

# 웹 접근성 및 성능 최적화

## 매 한 줄
> **"매 a11y 의 의 minority feature 의 의 — 매 keyboard / screen reader / high contrast user 의 의 majority 의 의 better UX."**. WCAG 2.2 (2023) + WCAG 3 (draft 2026) 의 의 standard, ARIA 1.3, Core Web Vitals (LCP/INP/CLS) 의 modern user-centric performance metric. 매 2026 의 의 INP (Interaction to Next Paint, 2024 replaced FID) 의 의 main interaction metric 의 의.

## 매 핵심

### 매 WCAG 2.2 의 4 principle (POUR)
- **Perceivable**: alt text, captions, contrast 4.5:1 (AA) / 7:1 (AAA).
- **Operable**: keyboard navigable, focus visible, no seizure-inducing flash.
- **Understandable**: clear language, error messages, predictable.
- **Robust**: valid HTML, ARIA properly used, works across AT.

### 매 Core Web Vitals (2026)
- **LCP (Largest Contentful Paint)**: < 2.5s — main content visible.
- **INP (Interaction to Next Paint)**: < 200ms — responsiveness (replaces FID).
- **CLS (Cumulative Layout Shift)**: < 0.1 — visual stability.

### 매 응용
1. Public sector — WCAG AA 의 의 (ADA, EU EN 301 549).
2. E-commerce — checkout 의 keyboard accessibility (2024 EAA mandate).
3. SEO — Core Web Vitals 의 Google ranking factor.
4. AI tooling — voice / dictation / screen reader user 의 의 의.

## 💻 패턴

### Semantic HTML + ARIA
```html
<!-- 매 BAD: div soup -->
<div class="button" onclick="submit()">Submit</div>

<!-- 매 GOOD: semantic + accessible -->
<button type="submit" aria-describedby="submit-help">
  Submit
</button>
<p id="submit-help" class="text-sm">매 reset 의 의 의.</p>
```

### Focus management (modal trap)
```tsx
import { useEffect, useRef } from 'react';
import FocusTrap from 'focus-trap-react';

export function Modal({ open, onClose, children }: Props) {
  const closeRef = useRef<HTMLButtonElement>(null);

  useEffect(() => {
    if (open) closeRef.current?.focus();
    const onKey = (e: KeyboardEvent) => e.key === 'Escape' && onClose();
    window.addEventListener('keydown', onKey);
    return () => window.removeEventListener('keydown', onKey);
  }, [open, onClose]);

  if (!open) return null;
  return (
    <FocusTrap>
      <div role="dialog" aria-modal="true" aria-labelledby="modal-title">
        <h2 id="modal-title">Settings</h2>
        {children}
        <button ref={closeRef} onClick={onClose}>Close</button>
      </div>
    </FocusTrap>
  );
}
```

### LCP optimization (image priority)
```tsx
// Next 15 의 의
import Image from 'next/image';

<Image
  src="/hero.webp"
  alt="Product showcase"
  width={1200}
  height={630}
  priority         // 매 LCP image 의 의 preload
  fetchPriority="high"
  sizes="(max-width: 768px) 100vw, 1200px"
/>
```

### INP optimization (yield to main thread)
```ts
// 매 long task 의 의 의 break up
async function processLargeList(items: Item[]) {
  const CHUNK = 100;
  for (let i = 0; i < items.length; i += CHUNK) {
    items.slice(i, i + CHUNK).forEach(process);
    // 매 yield to browser — keep INP < 200ms
    await scheduler.yield?.() ?? new Promise(r => setTimeout(r, 0));
  }
}

// React 19 useTransition
function Search() {
  const [isPending, startTransition] = useTransition();
  const [results, setResults] = useState([]);

  function onChange(q: string) {
    startTransition(() => {
      setResults(filter(largeList, q));  // 매 deprioritize
    });
  }
  return <input onChange={e => onChange(e.target.value)} />;
}
```

### CLS prevention (reserve space)
```css
/* 매 explicit aspect ratio — image / video 의 layout shift 의 */
.media {
  aspect-ratio: 16 / 9;
  width: 100%;
  background: #eee;
}

/* 매 font 의 layout shift — size-adjust + fallback metric */
@font-face {
  font-family: 'Inter';
  src: url('/inter.woff2') format('woff2');
  size-adjust: 107%;
  ascent-override: 90%;
  font-display: swap;
}
```

### Color contrast check
```ts
// 매 WCAG 의 의 contrast ratio
function contrastRatio(fg: string, bg: string): number {
  const lum = (hex: string) => {
    const [r, g, b] = hex.match(/\w\w/g)!.map(h => parseInt(h, 16) / 255);
    const lin = (c: number) =>
      c <= 0.03928 ? c / 12.92 : ((c + 0.055) / 1.055) ** 2.4;
    return 0.2126 * lin(r) + 0.7152 * lin(g) + 0.0722 * lin(b);
  };
  const [l1, l2] = [lum(fg), lum(bg)].sort((a, b) => b - a);
  return (l1 + 0.05) / (l2 + 0.05);  // ≥ 4.5 for AA, ≥ 7 for AAA
}
```

### Automated testing (axe-core + Playwright)
```ts
import { test, expect } from '@playwright/test';
import { injectAxe, checkA11y } from 'axe-playwright';

test('homepage 의 a11y', async ({ page }) => {
  await page.goto('/');
  await injectAxe(page);
  await checkA11y(page, undefined, {
    detailedReport: true,
    axeOptions: { runOnly: ['wcag2a', 'wcag2aa', 'wcag22aa'] },
  });
});
```

### Skip link + landmarks
```html
<a href="#main" class="skip-link">매 본문으로 건너뛰기</a>
<header role="banner">...</header>
<nav role="navigation" aria-label="Primary">...</nav>
<main id="main" tabindex="-1">...</main>
<footer role="contentinfo">...</footer>

<style>
.skip-link {
  position: absolute; left: -9999px;
}
.skip-link:focus {
  left: 0; top: 0; z-index: 100; padding: 1rem;
}
</style>
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Public sector / regulated | WCAG 2.2 AA mandatory + 3rd party audit |
| E-commerce | INP optimization (form/checkout) + keyboard nav |
| Marketing site | LCP < 2s + image priority + Next Image |
| SPA / dashboard | Focus management + ARIA live regions |
| Form-heavy | Error association (aria-describedby) + autocomplete |
| Animation-heavy | prefers-reduced-motion + INP budget |

**기본값**: Semantic HTML + axe-core CI + Lighthouse 의 LCP/INP/CLS budget + manual screen reader test (NVDA/VoiceOver) per release.

## 🔗 Graph
- 부모: [[Frontend Architecture]] · [[Web_Standards]]
- 변형: [[WCAG_2_2]] · [[ARIA]]
- 응용: [[Core Web Vitals Optimization (INP, LCP, CLS)|Core-Web-Vitals]] · [[Lighthouse]]

## 🤖 LLM 활용
**언제**: ARIA pattern lookup, semantic HTML refactor, WCAG criteria explanation, axe rule remediation.
**언제 X**: 의 actual screen reader UX evaluation (의 user testing 의 의), legal compliance ruling.

## ❌ 안티패턴
- **`<div onclick>`**: keyboard / screen reader 의 의.
- **Color-only signal**: red error 의 — icon / text label 의 의.
- **Auto-focus on load**: 매 disorienting — modal 의 의 의 의.
- **`outline: none` 의 focus state 의 X**: keyboard user 의 의 의 의.
- **Lazy-load LCP image**: 매 LCP 의 의 — `loading="eager"` + `fetchpriority="high"`.
- **`tabindex` 의 의 (>0)**: tab order 의 의 의.

## 🧪 검증 / 중복
- Verified (W3C WCAG 2.2 spec, web.dev Core Web Vitals, axe-core rules, MDN ARIA Authoring Practices).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — a11y + Core Web Vitals (INP) 의 의 |