Index: src/wp-admin/includes/update-core.php
===================================================================
--- src/wp-admin/includes/update-core.php	(revision 43907)
+++ src/wp-admin/includes/update-core.php	(working copy)
@@ -743,42 +743,45 @@
 'wp-includes/js/plupload/plupload.silverlight.xap',
 'wp-includes/js/swfupload/plugins',
 'wp-includes/js/swfupload/swfupload.swf',
-	// 4.9.2
-	'wp-includes/js/mediaelement/lang',
-	'wp-includes/js/mediaelement/lang/ca.js',
-	'wp-includes/js/mediaelement/lang/cs.js',
-	'wp-includes/js/mediaelement/lang/de.js',
-	'wp-includes/js/mediaelement/lang/es.js',
-	'wp-includes/js/mediaelement/lang/fa.js',
-	'wp-includes/js/mediaelement/lang/fr.js',
-	'wp-includes/js/mediaelement/lang/hr.js',
-	'wp-includes/js/mediaelement/lang/hu.js',
-	'wp-includes/js/mediaelement/lang/it.js',
-	'wp-includes/js/mediaelement/lang/ja.js',
-	'wp-includes/js/mediaelement/lang/ko.js',
-	'wp-includes/js/mediaelement/lang/nl.js',
-	'wp-includes/js/mediaelement/lang/pl.js',
-	'wp-includes/js/mediaelement/lang/pt.js',
-	'wp-includes/js/mediaelement/lang/ro.js',
-	'wp-includes/js/mediaelement/lang/ru.js',
-	'wp-includes/js/mediaelement/lang/sk.js',
-	'wp-includes/js/mediaelement/lang/sv.js',
-	'wp-includes/js/mediaelement/lang/uk.js',
-	'wp-includes/js/mediaelement/lang/zh-cn.js',
-	'wp-includes/js/mediaelement/lang/zh.js',
-	'wp-includes/js/mediaelement/mediaelement-flash-audio-ogg.swf',
-	'wp-includes/js/mediaelement/mediaelement-flash-audio.swf',
-	'wp-includes/js/mediaelement/mediaelement-flash-video-hls.swf',
-	'wp-includes/js/mediaelement/mediaelement-flash-video-mdash.swf',
-	'wp-includes/js/mediaelement/mediaelement-flash-video.swf',
-	'wp-includes/js/mediaelement/renderers/dailymotion.js',
-	'wp-includes/js/mediaelement/renderers/dailymotion.min.js',
-	'wp-includes/js/mediaelement/renderers/facebook.js',
-	'wp-includes/js/mediaelement/renderers/facebook.min.js',
-	'wp-includes/js/mediaelement/renderers/soundcloud.js',
-	'wp-includes/js/mediaelement/renderers/soundcloud.min.js',
-	'wp-includes/js/mediaelement/renderers/twitch.js',
-	'wp-includes/js/mediaelement/renderers/twitch.min.js',
+// 4.9.2
+'wp-includes/js/mediaelement/lang',
+'wp-includes/js/mediaelement/lang/ca.js',
+'wp-includes/js/mediaelement/lang/cs.js',
+'wp-includes/js/mediaelement/lang/de.js',
+'wp-includes/js/mediaelement/lang/es.js',
+'wp-includes/js/mediaelement/lang/fa.js',
+'wp-includes/js/mediaelement/lang/fr.js',
+'wp-includes/js/mediaelement/lang/hr.js',
+'wp-includes/js/mediaelement/lang/hu.js',
+'wp-includes/js/mediaelement/lang/it.js',
+'wp-includes/js/mediaelement/lang/ja.js',
+'wp-includes/js/mediaelement/lang/ko.js',
+'wp-includes/js/mediaelement/lang/nl.js',
+'wp-includes/js/mediaelement/lang/pl.js',
+'wp-includes/js/mediaelement/lang/pt.js',
+'wp-includes/js/mediaelement/lang/ro.js',
+'wp-includes/js/mediaelement/lang/ru.js',
+'wp-includes/js/mediaelement/lang/sk.js',
+'wp-includes/js/mediaelement/lang/sv.js',
+'wp-includes/js/mediaelement/lang/uk.js',
+'wp-includes/js/mediaelement/lang/zh-cn.js',
+'wp-includes/js/mediaelement/lang/zh.js',
+'wp-includes/js/mediaelement/mediaelement-flash-audio-ogg.swf',
+'wp-includes/js/mediaelement/mediaelement-flash-audio.swf',
+'wp-includes/js/mediaelement/mediaelement-flash-video-hls.swf',
+'wp-includes/js/mediaelement/mediaelement-flash-video-mdash.swf',
+'wp-includes/js/mediaelement/mediaelement-flash-video.swf',
+'wp-includes/js/mediaelement/renderers/dailymotion.js',
+'wp-includes/js/mediaelement/renderers/dailymotion.min.js',
+'wp-includes/js/mediaelement/renderers/facebook.js',
+'wp-includes/js/mediaelement/renderers/facebook.min.js',
+'wp-includes/js/mediaelement/renderers/soundcloud.js',
+'wp-includes/js/mediaelement/renderers/soundcloud.min.js',
+'wp-includes/js/mediaelement/renderers/twitch.js',
+'wp-includes/js/mediaelement/renderers/twitch.min.js',
+// 5.0.0
+'wp-includes/js/wp-a11y.js', // Moved to: wp-includes/js/dist/a11y.js
+'wp-includes/js/wp-a11y.min.js', // Moved to: wp-includes/js/dist/a11y.min.js
 );
 
 /**
Index: src/wp-includes/script-loader.php
===================================================================
--- src/wp-includes/script-loader.php	(revision 43907)
+++ src/wp-includes/script-loader.php	(working copy)
@@ -699,8 +699,6 @@
 		'expandMenu'   => __( 'Expand Main menu' ),
 	) );
 
-	$scripts->add( 'wp-a11y', "/wp-includes/js/wp-a11y$suffix.js", array( 'jquery' ), false, 1 );
-
 	$scripts->add( 'sack', "/wp-includes/js/tw-sack$suffix.js", array(), '1.6.1', 1 );
 
 	$scripts->add( 'quicktags', "/wp-includes/js/quicktags$suffix.js", array(), false, 1 );
Index: tests/phpunit/tests/dependencies/scripts.php
===================================================================
--- tests/phpunit/tests/dependencies/scripts.php	(revision 43907)
+++ tests/phpunit/tests/dependencies/scripts.php	(working copy)
@@ -668,12 +668,18 @@
 		global $wp_scripts;
 
 		wp_default_scripts( $wp_scripts );
+		wp_default_packages( $wp_scripts );
 
 		$wp_scripts->base_url  = '';
 		$wp_scripts->do_concat = true;
 
 		$ver = get_bloginfo( 'version' );
-		$expected  = "<script type='text/javascript' src='/wp-admin/load-scripts.php?c=0&amp;load%5B%5D=jquery-core,jquery-migrate,wp-a11y&amp;ver={$ver}'></script>\n";
+
+		$expected  = "\n<script type='text/javascript'>\n";
+		$expected .= "/* <![CDATA[ */\n";
+		$expected .= "( 'fetch' in window ) || document.write( '<script src=\"/wp-includes/js/dist/vendor/wp-polyfill-fetch.js\"></scr' + 'ipt>' );( document.contains ) || document.write( '<script src=\"/wp-includes/js/dist/vendor/wp-polyfill-node-contains.js\"></scr' + 'ipt>' );( window.FormData && window.FormData.prototype.keys ) || document.write( '<script src=\"/wp-includes/js/dist/vendor/wp-polyfill-formdata.js\"></scr' + 'ipt>' );( Element.prototype.matches && Element.prototype.closest ) || document.write( '<script src=\"/wp-includes/js/dist/vendor/wp-polyfill-element-closest.js\"></scr' + 'ipt>' );/* ]]> */\n";
+		$expected .= "</script>\n";
+		$expected .= "<script type='text/javascript' src='/wp-admin/load-scripts.php?c=0&amp;load%5B%5D=jquery-core,jquery-migrate,wp-polyfill,wp-dom-ready,wp-a11y&amp;ver={$ver}'></script>\n";
 		$expected .= "<script type='text/javascript'>\nconsole.log(\"before\");\n</script>\n";
 		$expected .= "<script type='text/javascript' src='http://example.com'></script>\n";
 		$expected .= "<script type='text/javascript' src='http://example2.com'></script>\n";
@@ -697,6 +703,7 @@
 		global $wp_scripts;
 
 		wp_default_scripts( $wp_scripts );
+		wp_default_packages( $wp_scripts );
 
 		$wp_scripts->base_url  = '';
 		$wp_scripts->do_concat = true;
Index: tests/qunit/index.html
===================================================================
--- tests/qunit/index.html	(revision 43907)
+++ tests/qunit/index.html	(working copy)
@@ -24,7 +24,7 @@
 			};
 		</script>
 		<script src="../../src/wp-includes/js/wp-util.js"></script>
-		<script src="../../src/wp-includes/js/wp-a11y.js"></script>
+		<script src="../../src/wp-includes/js/dist/a11y.js"></script>
 		<script>
 			window._wpMediaModelsL10n = {"settings":{"ajaxurl":"\/wp-admin\/admin-ajax.php","post":{"id":0}}};
 		</script>