docs(10_Wiki): W3Schools 위키화 — HTML/CSS/JavaScript(core)
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>
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id: css-structural-pseudo-classes
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title: "CSS Structural Pseudo-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: ["structural pseudo-classes", ":first-child", ":lang", "nth-child", "position-based selectors", "tree-position selectors"]
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duplicate_of: ""
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source_trust_level: "B"
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confidence_score: 0.87
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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: ["css", "web", "frontend", "w3schools", "pseudo-classes", "selectors"]
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raw_sources: ["https://www.w3schools.com/css/css_pseudo_classes_structural.asp"]
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applied_in: []
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github_commit: ""
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---
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# [[CSS Structural Pseudo-classes]]
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## 🎯 한 줄 통찰 (One-line insight)
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Structural pseudo-classes select elements based on their position in the document tree, letting you target things like the first child or language-tagged elements without adding extra classes. [S1]
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## 🧠 핵심 개념 (Core concepts)
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- **Definition** — Structural pseudo-classes select elements based on their position in the document tree. [S1]
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- **`:first-child`** — Matches an element that is the first child of another element. [S1]
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- **`:lang()`** — Used to select elements with a `lang` attribute set to the specified value. [S1]
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- **Position is relative to the parent** — selection depends on where the element sits among its siblings, not on a class or id. [S1]
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## 🧩 추출된 패턴 (Extracted patterns)
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- **First-child targeting** — `selector:first-child` styles only the element that appears first inside its parent. [S1]
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- **Combining position with descent** — `p em:first-child` vs `p:first-child em` produce different results depending on which element the `:first-child` is attached to. [S1]
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- **Language-aware styling** — `:lang(code)` applies styles (e.g. quotation marks) only to elements carrying a matching `lang` value. [S1]
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## 📖 세부 내용 (Details)
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**Introduction** [S1]
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Structural pseudo-classes select elements based on their position in the document tree.
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**The `:first-child` pseudo-class** [S1]
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The `:first-child` pseudo-class matches a specified element that is the first child of another element.
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Style all first child `<p>` elements:
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```css
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p:first-child {
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color: blue;
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}
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```
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Style the first `<em>` element in all `<p>` elements:
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```css
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p em:first-child {
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color: blue;
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}
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```
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Style all `<em>` elements in all first child `<p>` elements:
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```css
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p:first-child em {
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color: blue;
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}
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```
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**The `:lang()` pseudo-class** [S1]
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The `:lang()` pseudo-class is used to select elements with a `lang` attribute with the specified value.
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Define quotation marks for `<q>` elements with `lang="no"` (Norwegian):
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```html
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<html>
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<head>
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<style>
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q:lang(no) {
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quotes: "~" "~";
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}
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</style>
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</head>
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<body>
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<p>Some text <q lang="no">A quote in a paragraph</q> Some text.</p>
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</body>
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</html>
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```
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**Other structural pseudo-classes** [S1]
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| Pseudo-class | Description |
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| --- | --- |
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| `:last-child` | Matches the last child of a parent |
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| `:nth-child(n)` | Matches the nth child of a parent |
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| `:nth-last-child(n)` | Matches the nth child from the end |
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| `:only-child` | Matches an element that is the only child |
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| `:first-of-type` | Matches the first element of its type |
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| `:last-of-type` | Matches the last element of its type |
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For a complete list, the source directs readers to the CSS Pseudo-classes Reference. [S1]
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## 🛠️ 적용 사례 (Applied in summary)
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The page's own applied examples are the `:first-child` rules (blue paragraphs / emphasized text) and the Norwegian `:lang(no)` quotation-mark demo. No external project/commit applications found in the source.
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## 💻 코드 패턴 (Code patterns)
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First-child selector (language: CSS):
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```css
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p:first-child {
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color: blue;
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}
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```
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Language selector (language: CSS):
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```css
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q:lang(no) {
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quotes: "~" "~";
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}
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```
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## ⚖️ 모순 및 업데이트 (Contradictions & updates)
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No contradictions found in the source.
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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:** 0.87
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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:** [[CSS Tutorial]]
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- **관련 개념:** [[CSS Pseudo-elements]], [[CSS Selectors]], [[CSS Combinators]]
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- **참조 맥락:** Referenced when targeting elements by their tree position instead of adding extra classes.
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## 📚 출처 (Sources)
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- [S1] W3Schools — CSS Structural Pseudo-classes — https://www.w3schools.com/css/css_pseudo_classes_structural.asp
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## 📝 변경 이력 (Change history)
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- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Structural Pseudo-classes" page (Astra wiki-curation, P-Reinforce v3.1 format).
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