Index: wp-content/themes/twentyfifteen/js/functions.js
===================================================================
--- wp-content/themes/twentyfifteen/js/functions.js	(revision 31794)
+++ wp-content/themes/twentyfifteen/js/functions.js	(working copy)
@@ -60,7 +60,11 @@
 		} );
 	} )();
 
-	// Add or remove ARIA attributes.
+	/**
+	 * @summary Add or remove ARIA attributes.
+	 * Uses jQuery's $window.width() to determine the size of the window and add the default ARIA attributes for the menu toggle if it's on screen.
+	 * @since 4.2
+	 */
 	function onResizeARIA() {
 		if ( 955 > $window.width() ) {
 			button.attr( 'aria-expanded', 'false' );