[css-borders-4] Add 'hairline' keyword to <line-width>. w3c/csswg-drafts@fb330e9

Author: triple-underscore

css-borders-ja.html

@@ -215,8 +215,8 @@
 ●●options
 
 spec_title:CSS Borders and Box Decorations Module Level 4
-spec_date:2026-02-18
-trans_update:2026-02-21
+spec_date:2026-03-04
+trans_update:2026-03-06
 source_checked:251021
 page_state_key:CSS
 original_url:https://drafts.csswg.org/css-borders-4/
@@ -611,6 +611,7 @@
 v.inset:#valdef-line-style-inset
 v.outset:#valdef-line-style-outset
 
+v.hairline:#valdef-line-width-hairline
 v.thick:#valdef-line-width-thick
 v.medium:#valdef-line-width-medium
 v.thin:#valdef-line-width-thin
@@ -1268,6 +1269,7 @@
 外見:look:~
 見かけ:look:~
 touch::::タッチ
+zoom::::ズーム
 	~scroll可能:scrollable
 
 	●仕様
@@ -1389,6 +1391,9 @@
 	ほぼ／ほとんど:nearly
 	形状を違えることを除き:except insofar as it shapes 〜 differently
 	ずっと高速になる:result in an effect where 〜 much higher velocity
+	整数倍:integer number of
+	およそ:approximately
+	ちょうど〜になる:just
 
 ●●images
 ＠css-borders/
@@ -1424,9 +1429,9 @@
 [CSS-CASCADE-5]
     Elika Etemad; Miriam Suzanne; Tab Atkins Jr.. ＜CSS Cascading and Inheritance Level 5＞. 13 January 2022. CR. URL: https://www.w3.org/TR/css-cascade-5/
 [CSS-COLOR-4]
-    Chris Lilley; Tab Atkins Jr.; Lea Verou. ＜CSS Color Module Level 4＞. 24 April 2025. CRD. URL: https://www.w3.org/TR/css-color-4/
+    Tab Atkins Jr.; Chris Lilley; Lea Verou. ＜CSS Color Module Level 4＞. 27 February 2026. CRD. URL: https://www.w3.org/TR/css-color-4/
 [CSS-COLOR-5]
-    Chris Lilley; et al. ＜CSS Color Module Level 5＞. 13 January 2026. WD. URL: https://www.w3.org/TR/css-color-5/
+    Chris Lilley; Una Kravets; Lea Verou. ＜CSS Color Module Level 5＞. 27 February 2026. WD. URL: https://www.w3.org/TR/css-color-5/
 [CSS-DISPLAY-4]
     Elika Etemad; Tab Atkins Jr.. ＜CSS Display Module Level 4＞. 6 November 2025. WD. URL: https://www.w3.org/TR/css-display-4/
 [CSS-GRID-2]
@@ -2406,6 +2411,7 @@ <h3 title="Line Thickness: the border-width properties">2.3. 線の太さ： `bo
 <pre class="prod">
 `line-width@t
 	= `length [0,∞]$t
+	| `hairline$v
 	| `thin$v
 	| `medium$v
 	| `thick$v
@@ -2421,8 +2427,15 @@ <h3 title="Line Thickness: the border-width properties">2.3. 線の太さ： `bo
 `thick@v
 は `5px^v
 ］と等価になるとする。
+~keyword
+`hairline@v
+は、
+~UA定義な `1px^v 以下の長さであり，
+既定の~page~zoomにおける機器~画素の整数倍に等しい “ちょうど可視になる” 線を表現する
+（その大きさは， `1px^v ほどにもなり得るが、
+多くの機器では，およそ `0.3px^v 〜 `0.5px^v になる）。
 ◎
-Negative values are invalid. The thin, medium, and thick keywords are equivalent to 1px, 3px, and 5px, respectively.
+Negative values are invalid. The thin, medium, and thick keywords are equivalent to 1px, 3px, and 5px, respectively. The hairline keyword is a UA-defined length, less than or equal to 1px and equal to an integer number of device pixels at the default page zoom, which represents a "just visible" line. (While it can be as large as 1px, on many devices it will be approximately 0.3px to 0.5px.)
 </p>
 
 <p>