[css-display] typo

Author: tabatkins

css-display-3/Overview.bs

@@ -93,7 +93,7 @@ Introduction</h2>
 	Similarly, each contiguous sequence of sibling <a>text nodes</a> generates a <a>text run</a>,
 	which is assigned the same styles as the generating <a>text nodes</a>.
 
-	An <dfn for=CSS lt="anonymous|anonymous box" export>anonymous box</dfn> is is a box that is not associated with any element.
+	An <dfn for=CSS lt="anonymous|anonymous box" export>anonymous box</dfn> is a box that is not associated with any element.
 	<a>Anonymous boxes</a> are generated in certain circumstances
 	to fix up the <a>box tree</a> when it requires a particular nested structure
 	that is not provided by the boxes generated from the <a>element tree</a>.