[css-inline-3] Define how text-box-trim applies to multicol containers. #5335

Author: fantasai

css-inline-3/Overview.bs

@@ -1405,6 +1405,7 @@ Trimming Over/Under Text: the 'text-box-trim' property</h3>
 	to match the specified 'text-box-edge' metric.
 
 	On [=block containers=],
+	as well as on each column of a [=multi-column container=],
 	specifies whether to trim [=half-leading=]
 	at the start/end of its content
 	to the specified 'text-box-edge' metric
@@ -1425,7 +1426,7 @@ Trimming Over/Under Text: the 'text-box-trim' property</h3>
 
 		<dt><dfn>trim-start</dfn>
 		<dd>
-			For [=block containers=]:
+			For [=block containers=] and [=column boxes=]:
 			trim the [=block-start=] side of the <a>first formatted line</a>
 			to the specified metric of its [=root inline box=].
 			If there is no such line,
@@ -1438,7 +1439,7 @@ Trimming Over/Under Text: the 'text-box-trim' property</h3>
 
 		<dt><dfn>trim-end</dfn>
 		<dd>
-			For [=block containers=]:
+			For [=block containers=] and [=column boxes=]:
 			trim the [=block-end=] side of the last formatted line
 			to the specified metric of its [=root inline box=].
 			If there is no such line,
@@ -3050,6 +3051,12 @@ A.3: Synthesizing Baselines for Atomic Inlines</h3>
 <h2 class="no-num" id="changes">
 Changes</h2>
 
+	Changes since the <a href="https://www.w3.org/TR/2024/WD-css-inline-3-20240812/">12 August 2024 Working Draft</a>:
+	<ul>
+		<li>Defined behavior of 'text-box-trim' on [=multi-column containers=].
+			(<a href="https://github.com/w3c/csswg-drafts/issues/5335">Issue 5335</a>)
+	</ul>
+
 	Changes since the
 	<a href="https://www.w3.org/TR/2024/WD-css-inline-3-20240808/">8 August 2024 Working Draft</a>:
 	<ul>