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>
2026-06-23 19:21:18 +09:00
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+---
+id: css-masking-with-svg
+title: "CSS Masking with SVG"
+category: "Frontend"
+status: "draft"
+verification_status: "conceptual"
+canonical_id: ""
+aliases: ["SVG mask", "svg mask element", "mask-image svg", "CSS masking SVG", "svg clip shapes"]
+duplicate_of: ""
+source_trust_level: "B"
+confidence_score: 0.87
+created_at: 2026-06-23
+updated_at: 2026-06-23
+review_reason: ""
+merge_history: []
+tags: ["css", "web", "frontend", "w3schools", "masking", "svg", "mask-image"]
+raw_sources: ["https://www.w3schools.com/css/css3_masking_svg.asp"]
+applied_in: []
+github_commit: ""
+---
+
+# [[CSS Masking with SVG]]
+
+## 🎯 한 줄 통찰 (One-line insight)
+An SVG `<mask>` element can act as a mask layer for an image, using SVG shapes (circle, ellipse, polygon) to define which parts of the image are revealed. [S1]
+
+## 🧠 핵심 개념 (Core concepts)
+- **SVG mask layer** — an SVG `<mask>` element can serve as the mask layer applied to an image. [S1]
+- **Shape-driven** — the visible region is defined by SVG shapes (`<circle>`, `<ellipse>`, `<polygon>`) filled with `#ffffff` inside the mask. [S1]
+- **Wiring** — the image references the mask via `mask="url(#svgmask1)"`, where the id matches the `<mask>` element's id. [S1]
+
+## 🧩 추출된 패턴 (Extracted patterns)
+- **Define-then-reference** — declare a `<mask id="...">` containing white-filled shapes, then point the `<image>`'s `mask` attribute at `url(#id)`. [S1]
+- **Composite masks** — multiple shapes (e.g. several `<circle>`s) inside one `<mask>` reveal multiple regions at once. [S1]
+
+## 📖 세부 내용 (Details)
+This page demonstrates how to apply SVG mask layers to images using various SVG shapes. Each example defines an SVG `<mask>` with one or more white-filled (`#ffffff`) shapes, then applies it to an `<image>` via `mask="url(#svgmask1)"`. [S1]
+
+**Circle mask** [S1]
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <circle r="150" cx="200" cy="200" fill="#ffffff" />
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+**Ellipse mask** [S1]
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <ellipse cx="220" cy="150" rx="200" ry="100" fill="#ffffff" />
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+**Triangle mask** [S1]
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <polygon fill="#ffffff" points="200 0, 400 400, 0 400"></polygon>
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+**Star mask** [S1]
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <polygon fill="#ffffff" points="100,10 40,198 190,78 10,78 160,198"></polygon>
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+**Multiple circles mask** [S1]
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <circle fill="#ffffff" cx="75" cy="75" r="75"></circle>
+    <circle fill="#ffffff" cx="80" cy="260" r="75"></circle>
+    <circle fill="#ffffff" cx="270" cy="160" r="75"></circle>
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+**CSS masking properties reference** [S1]
+
+| Property | Description |
+|---|---|
+| `mask-clip` | Specifies which area is affected by a mask image |
+| `mask-composite` | Specifies a compositing operation used on the current mask layer with the mask layers below it |
+| `mask-image` | Specifies an image to be used as a mask layer for an element |
+| `mask-mode` | Specifies whether the mask layer image is treated as a luminance mask or as an alpha mask |
+| `mask-origin` | Specifies the origin position (the mask position area) of a mask layer image |
+| `mask-position` | Sets the starting position of a mask layer image (relative to the mask position area) |
+| `mask-repeat` | Specifies how the mask layer image is repeated |
+| `mask-size` | Specifies the size of a mask layer image |
+| `mask-type` | Specifies whether an SVG `<mask>` element is treated as a luminance mask or as an alpha mask |
+
+## 🛠️ 적용 사례 (Applied in summary)
+The page's own examples are the applied cases: SVG `<mask>` layers (circle, ellipse, triangle, star, multiple circles) applied to the `img_5terre.jpg` image. No external project/commit applications found in the source.
+
+## 💻 코드 패턴 (Code patterns)
+Reveal a circular region of an image with an SVG mask (language: HTML/SVG):
+```html
+<svg width="600" height="400" xmlns="http://www.w3.org/2000/svg">
+  <mask id="svgmask1">
+    <circle r="150" cx="200" cy="200" fill="#ffffff" />
+  </mask>
+  <image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="img_5terre.jpg" mask="url(#svgmask1)"></image>
+</svg>
+```
+
+## ⚖️ 모순 및 업데이트 (Contradictions & updates)
+No contradictions found in the source.
+
+## ✅ 검증 상태 및 신뢰도
+- **상태:** draft
+- **검증 단계:** conceptual (실제 적용 사례 발견 시 applied/validated로 승격 가능)
+- **출처 신뢰도:** B (W3Schools — widely used educational reference, not a primary standards body)
+- **신뢰 점수:** 0.87
+- **중복 검사 결과:** 신규 생성 (New discovery)
+
+## 🔗 지식 그래프 (Knowledge Graph)
+- **상위/루트:** [[CSS Tutorial]]
+- **관련 개념:** [[CSS Masking PNG]], [[CSS Masking Gradients]], [[CSS Image Shapes]]
+- **참조 맥락:** Referenced when masking an image to arbitrary shapes defined by SVG geometry.
+
+## 📚 출처 (Sources)
+- [S1] W3Schools — CSS Masking with SVG — https://www.w3schools.com/css/css3_masking_svg.asp
+
+## 📝 변경 이력 (Change history)
+- 2026-06-23: Initial draft synthesized from the W3Schools "CSS Masking with SVG" page (Astra wiki-curation, P-Reinforce v3.1 format).