[css-inline-3] Use innermost trim when multiple apply #5426

Author: fantasai

css-inline-3/Overview.bs

@@ -1463,6 +1463,10 @@ Trimming Over/Under Text: the 'text-box-trim' property
 	Note: The [=block-end=] side does not coincide with the [=line-under=] side
 	when 'writing-mode' is ''vertical-lr''.
 
+	If multiple ancestors specify trimming on the same [=line box=],
+	the metric used is that of the innermost [=block container=]
+	that requests trimming on that side of the [=line box=].
+
 	Note: Content and ink overflowing a box
 	due to non-initial values of 'text-box-trim'
 	is handled the same as content that would overflow the box or line box otherwise.
@@ -3059,6 +3063,9 @@ Changes
 			and 'line-fit-edge' for controlling line box sizing.
 			(Issues 8829
 			and 8696)
+		Use the innermost trim edge for 'text-box-trim'
+			when multiple ancestors request trimming.
+			(Issue 5426)
 		Apply negative [=block-axis=] margins to descendants of [=inline boxes=]
 			when calculating their [=layout bounds=]
 			so that they can actually have the specified effect.