[css-overflow-3] Interaction of block-ellipsis and first-line/first-letter

Closes #2906

Author: frivoal

css-overflow-3/Overview.bs

@@ -859,7 +859,8 @@ Indicating Block-Axis Overflow: the 'block-ellipsis' property</h3>
 	and measures the inserted <a>block overflow ellipsis</a>
 	together with the rest of the line’s content.
 
-	Issue(2906): Interaction with ''::first-letter'' and ''::first-line'' needs to be defined.
+	The [=block overflow ellipsis=] must not be included
+	in either the ''::first-letter'' nor the ''::first-line'' pseudo-elements.
 
 	If there is no next <a>fragmentation container</a>
 	and thus the remainder of the content after the break would be discarded,