[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
 	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
 
 		trim-start
 		
-			For [=block containers=]:
+			For [=block containers=] and [=column boxes=]:
 			trim the [=block-start=] side of the first formatted line
 			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
 
 		trim-end
 		
-			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
 
 Changes
 
+	Changes since the 12 August 2024 Working Draft:
+	
+		Defined behavior of 'text-box-trim' on [=multi-column containers=].
+			(Issue 5335)
+	
+
 	Changes since the
 	8 August 2024 Working Draft: