[css-overflow-4] Define where the line clamp can be around floats (w3c#13528)

Closes w3c#12817.

Author: andreubotella

css-overflow-4/Overview.bs

@@ -1539,8 +1539,18 @@ Handling of Excess Content: the 'continue' property</h3>
 			webkit-line-clamp-040.html
 		</wpt>
 
+		For this definition,
+		[=out-of-flow=] boxes between two line boxes
+		don't prevent them from being consecutive.
+		This is the case even if
+		the second line box is pushed down by [=floats=].
+		Such out-of-flow boxes are considered
+		to be after the clamp point.
+
 	- A point between two [=in-flow=] [=block-level=] sibling boxes
 		in the line-clamp container's [=block formatting context=].
+		Any [=out-of-flow=] boxes in between are considered
+		to be after the clamp point.
 
 		<wpt>
 			line-clamp-auto-034.html