[css-overflow-3] Clarify relationship of block overflow ellipsis to block container.

Author: fantasai

css-overflow-3/Overview.bs

@@ -635,9 +635,9 @@ Indicating Block-Axis Overflow: the 'block-overflow' property</h2>
 	the <a>block overflow ellipsis</a>
 	is wrapped in an anonymous inline
 	and placed at the end of the line box
-	as a direct child of its containing block,
-	effectively shortening the line box
-	from the perspective of the remaining contents of the line.
+	as a direct child of the <a>block container</a>’s <a>root inline box</a>,
+	reducing the space in the line box
+	available to the other contents of the line.
 	This inline is assigned ''unicode-bidi: plaintext''
 	and is placed in the line box after the last
 	<a>soft wrap opportunity</a> [[!CSS-TEXT-3]]