[css-multicol-1] exporting dfn

Author: rachelandrew

css-multicol-1/Overview.bs

@@ -1118,7 +1118,7 @@ Pagination and overflow outside multicol containers</h3>
 	</ul>
 
 	Columns that appear outside the multicol container in continuous contexts
-	are called <dfn>overflow columns</dfn>. Overflow columns can effect the height of the multicol container.
+	are called <dfn export>overflow columns</dfn>. Overflow columns can effect the height of the multicol container.
 
 	<div class="example">
 		In this example, the height of the multi-column container has been