Index: src/wp-admin/js/common.js
===================================================================
--- src/wp-admin/js/common.js	(revision 26862)
+++ src/wp-admin/js/common.js	(working copy)
@@ -557,6 +557,12 @@
 			$( '#wp-admin-bar-menu-toggle' ).on( 'click.wp-responsive', function( event ) {
 				event.preventDefault();
 				$wpwrap.toggleClass( 'wp-responsive-open' );
+				if ( $wpwrap.hasClass( 'wp-responsive-open' ) ) {
+					$(this).find('a').attr( 'aria-expanded', 'true' );
+					$( '#adminmenu a:first' ).focus();
+				} else {
+					$(this).find('a').attr( 'aria-expanded', 'false' );
+				}
 			} );
 
 			// Add menu events
Index: src/wp-includes/admin-bar.php
===================================================================
--- src/wp-includes/admin-bar.php	(revision 26862)
+++ src/wp-includes/admin-bar.php	(working copy)
@@ -166,10 +166,10 @@
 	if ( is_admin() ) {
 		$wp_admin_bar->add_menu( array(
 			'id'    => 'menu-toggle',
-			'title' => '<span class="ab-icon"></span>',
+			'title' => '<span class="ab-icon" aria-hidden="true"></span><span class="screen-reader-text">' . __( 'Menu' ) . '</span>',
 			'href'  => '#',
 			'meta'  => array(
-				'title' => __( 'Menu' ),
+				'expandable' => true,
 			),
 		) );
 	}
Index: src/wp-includes/class-wp-admin-bar.php
===================================================================
--- src/wp-includes/class-wp-admin-bar.php	(revision 26862)
+++ src/wp-includes/class-wp-admin-bar.php	(working copy)
@@ -409,7 +409,12 @@
 		$has_link  = ! empty( $node->href );
 
 		$tabindex = isset( $node->meta['tabindex'] ) ? (int) $node->meta['tabindex'] : '';
+		$expandable = isset( $node->meta['expandable'] ) ? (bool) $node->meta['expandable'] : false;
+		
 		$aria_attributes = $tabindex ? 'tabindex="' . $tabindex . '"' : '';
+		if ( $expandable ) {
+			$aria_attributes .= ' aria-expanded="false"';
+		}
 
 		$menuclass = '';