[css-multicol] Spanners establish new FCs, not necessarily BFCs

Author: frivoal

css-multicol-1/Overview.bs

@@ -895,7 +895,7 @@ h2 {
 	</div>
 
 	<div class="example">
-		Spanners create new block formatting contexts, but their margins
+		Spanners establish new formatting contexts, but their margins
 		can be changed by their surroundings. In this example, two spanners
 		naturally end up at the top of a page. The top margin of the first
 		spanner is truncated due to adjoining an unforced break. The margins