[css-inline-3] Use innermost trim when multiple apply w3c#5426

Author: fantasai

css-inline-3/Overview.bs

@@ -1463,6 +1463,10 @@ Trimming Over/Under Text: the 'text-box-trim' property</h3>
 	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</h2>
 			and 'line-fit-edge' for controlling line box sizing.
 			(Issues <a href="https://github.com/w3c/csswg-drafts/issues/8829">8829</a>
 			and <a href="https://github.com/w3c/csswg-drafts/issues/8696">8696</a>)
+		<li>Use the innermost trim edge for 'text-box-trim'
+			when multiple ancestors request trimming.
+			(<a href="https://github.com/w3c/csswg-drafts/issues/5426">Issue 5426</a>)
 		<li>Apply negative [=block-axis=] margins to descendants of [=inline boxes=]
 			when calculating their [=layout bounds=]
 			so that they can actually have the specified effect.