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W3Schools 튜토리얼을 P-Reinforce v3.1 포맷으로 위키화(영어 본문, 한/영 섹션 헤더). - Topic_HTML: 59문서 (튜토리얼+예제, 레퍼런스/메타 제외) - Topic_CSS: 190문서 (메인 + Advanced/Flexbox/Grid/RWD 전체) - Topic_JavaScript: 120문서 (코어 언어; Temporal/DOM상세/BOM/WebAPI/AJAX/jQuery/Graphics 등은 후속) 각 폴더 00_INDEX.md(MOC) 포함. 코드 verbatim, 미확인분은 "Not found in source" 표기. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
206 lines
6.6 KiB
Markdown
206 lines
6.6 KiB
Markdown
---
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id: html-classes
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title: "HTML Classes"
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category: "Frontend"
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status: "draft"
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verification_status: "conceptual"
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canonical_id: ""
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aliases: ["class attribute", "HTML class", "CSS class selector", "getElementsByClassName", "multiple classes"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.90
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created_at: 2026-06-23
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updated_at: 2026-06-23
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review_reason: ""
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merge_history: []
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tags: ["html", "web", "frontend", "w3schools", "css"]
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raw_sources: ["https://www.w3schools.com/html/html_classes.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[HTML Classes]]
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## 🎯 한 줄 통찰 (One-line insight)
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The HTML `class` attribute assigns one or more class names to elements so CSS and JavaScript can select and act on a whole group of elements at once. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Purpose** — the `class` attribute is often used to point to a class name in a style sheet; it can also be used by JavaScript to access and manipulate elements with the specific class name. [S1]
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- **CSS selector** — in a stylesheet a class is referenced with a period (e.g. `.city`). [S1]
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- **Shared by many elements** — multiple HTML elements can share the same class. [S1]
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- **Multiple classes per element** — separate class names with a space (e.g. `class="city main"`); the element is styled according to all classes specified. [S1]
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- **Works across element types** — different HTML elements can point to the same class name. [S1]
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- **JavaScript access** — `getElementsByClassName()` returns all elements with a given class name. [S1]
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- **Usable anywhere** — the `class` attribute can be used on any HTML element, and the class name is case sensitive. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **Shared-style pattern** — give several elements the same class so one CSS rule styles them all. [S1]
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- **Multi-class pattern** — combine general and specific classes on one element (`class="city main"`). [S1]
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- **Inline-styling pattern** — apply a class to a `<span>` to style a fragment of text. [S1]
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- **JS-grouping pattern** — collect and manipulate all elements of a class with `getElementsByClassName()`. [S1]
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## 📖 세부 내용 (Details)
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**The class Attribute.** The `class` attribute is often used to point to a class name in a style sheet. It can also be used by JavaScript to access and manipulate elements with the specific class name. [S1]
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Basic class with CSS styling — three headings share the `city` class: [S1]
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```html
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<!DOCTYPE html>
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<html>
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<head>
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<style>
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.city {
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background-color: tomato;
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color: white;
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padding: 10px;
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}
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</style>
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</head>
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<body>
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<h2 class="city">London</h2>
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<p>London is the capital of England.</p>
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<h2 class="city">Paris</h2>
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<p>Paris is the capital of France.</p>
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<h2 class="city">Tokyo</h2>
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<p>Tokyo is the capital of Japan.</p>
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</body>
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</html>
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```
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**Using the class attribute on `<div>` elements.** [S1]
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```html
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<!DOCTYPE html>
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<html>
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<head>
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<style>
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.city {
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background-color: tomato;
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color: white;
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border: 2px solid black;
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margin: 20px;
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padding: 20px;
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}
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</style>
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</head>
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<body>
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<div class="city">
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<h2>London</h2>
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<p>London is the capital of England.</p>
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</div>
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<div class="city">
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<h2>Paris</h2>
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<p>Paris is the capital of France.</p>
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</div>
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<div class="city">
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<h2>Tokyo</h2>
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<p>Tokyo is the capital of Japan.</p>
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</div>
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</body>
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</html>
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```
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**The class attribute on inline (`<span>`) elements.** [S1]
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```html
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<!DOCTYPE html>
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<html>
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<head>
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<style>
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.note {
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font-size: 120%;
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color: red;
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}
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</style>
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</head>
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<body>
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<h1>My <span class="note">Important</span> Heading</h1>
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<p>This is some <span class="note">important</span> text.</p>
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</body>
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</html>
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```
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**Multiple Classes.** HTML elements can belong to more than one class. To define multiple classes, separate the class names with a space, e.g. `<div class="city main">`. The element will be styled according to all the classes specified. [S1]
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```html
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<h2 class="city main">London</h2>
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<h2 class="city">Paris</h2>
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<h2 class="city">Tokyo</h2>
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```
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**Different Elements Can Share Same Class.** Different HTML elements can point to the same class name. [S1]
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```html
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<h2 class="city">Paris</h2>
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<p class="city">Paris is the capital of France</p>
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```
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**Using the class Attribute in JavaScript.** JavaScript can access elements with a specific class name by using the `getElementsByClassName()` method. [S1]
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```javascript
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<script>
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function myFunction() {
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var x = document.getElementsByClassName("city");
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for (var i = 0; i < x.length; i++) {
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x[i].style.display = "none";
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}
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}
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</script>
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```
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> **Tip:** The `class` attribute can be used on **any** HTML element. [S1]
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> **Note:** The class name is case sensitive! [S1]
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**Chapter Summary.** [S1]
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- The HTML `class` attribute specifies one or more class names for an element.
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- Classes are used by CSS and JavaScript to select and access specific elements.
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- The `class` attribute can be used on any HTML element.
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- The class name is case sensitive.
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- Different HTML elements can point to the same class name.
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- JavaScript can access elements with a specific class name with the `getElementsByClassName()` method.
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## 🛠️ 적용 사례 (Applied in summary)
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The shared `city` class (across headings, divs, and paragraphs), the multi-class `city main` heading, and the `getElementsByClassName("city")` hide-function are the canonical applied examples. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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Define and apply a class (HTML + CSS):
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```html
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<style>
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.city { color: white; }
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</style>
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<h2 class="city">London</h2>
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```
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Multiple classes (HTML):
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```html
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<div class="city main">...</div>
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```
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Select by class in JavaScript:
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```javascript
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var x = document.getElementsByClassName("city");
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```
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source. [S1]
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## ✅ 검증 상태 및 신뢰도
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- **상태:** draft
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- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
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- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
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- **신뢰 점수:** 0.90
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- **중복 검사 결과:** 신규 생성 (New discovery)
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## 🔗 지식 그래프 (Knowledge Graph)
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- **상위/루트:** [[HTML Tutorial]]
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- **관련 개념:** [[HTML Id]], [[HTML Div]], [[HTML Block and Inline]], [[HTML JavaScript]]
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- **참조 맥락:** Referenced whenever a group of elements must share styling or be selected together by CSS or JavaScript.
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## 📚 출처 (Sources)
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- [S1] W3Schools — HTML Classes — https://www.w3schools.com/html/html_classes.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "HTML Classes" page (Astra wiki-curation, P-Reinforce v3.1 format).
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