diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/widgets/class-wp-widget-recent-comments.php
--- a/wp/wp-includes/widgets/class-wp-widget-recent-comments.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/widgets/class-wp-widget-recent-comments.php	Tue Dec 15 13:49:49 2020 +0100
@@ -49,32 +49,41 @@
 		 * @param bool   $active  Whether the widget is active. Default true.
 		 * @param string $id_base The widget ID.
 		 */
-		if ( ! current_theme_supports( 'widgets' ) // Temp hack #14876
+		if ( ! current_theme_supports( 'widgets' ) // Temp hack #14876.
 			|| ! apply_filters( 'show_recent_comments_widget_style', true, $this->id_base ) ) {
 			return;
 		}
-		?>
-		<style type="text/css">.recentcomments a{display:inline !important;padding:0 !important;margin:0 !important;}</style>
-		<?php
+
+		$type_attr = current_theme_supports( 'html5', 'style' ) ? '' : ' type="text/css"';
+
+		printf(
+			'<style%s>.recentcomments a{display:inline !important;padding:0 !important;margin:0 !important;}</style>',
+			$type_attr
+		);
 	}
 
 	/**
 	 * Outputs the content for the current Recent Comments widget instance.
 	 *
 	 * @since 2.8.0
+	 * @since 5.4.0 Creates a unique HTML ID for the `<ul>` element
+	 *              if more than one instance is displayed on the page.
 	 *
 	 * @param array $args     Display arguments including 'before_title', 'after_title',
 	 *                        'before_widget', and 'after_widget'.
 	 * @param array $instance Settings for the current Recent Comments widget instance.
 	 */
 	public function widget( $args, $instance ) {
+		static $first_instance = true;
+
 		if ( ! isset( $args['widget_id'] ) ) {
 			$args['widget_id'] = $this->id;
 		}
 
 		$output = '';
 
-		$title = ( ! empty( $instance['title'] ) ) ? $instance['title'] : __( 'Recent Comments' );
+		$default_title = __( 'Recent Comments' );
+		$title         = ( ! empty( $instance['title'] ) ) ? $instance['title'] : $default_title;
 
 		/** This filter is documented in wp-includes/widgets/class-wp-widget-pages.php */
 		$title = apply_filters( 'widget_title', $title, $instance, $this->id_base );
@@ -84,18 +93,18 @@
 			$number = 5;
 		}
 
-		/**
-		 * Filters the arguments for the Recent Comments widget.
-		 *
-		 * @since 3.4.0
-		 * @since 4.9.0 Added the `$instance` parameter.
-		 *
-		 * @see WP_Comment_Query::query() for information on accepted arguments.
-		 *
-		 * @param array $comment_args An array of arguments used to retrieve the recent comments.
-		 * @param array $instance     Array of settings for the current widget.
-		 */
 		$comments = get_comments(
+			/**
+			 * Filters the arguments for the Recent Comments widget.
+			 *
+			 * @since 3.4.0
+			 * @since 4.9.0 Added the `$instance` parameter.
+			 *
+			 * @see WP_Comment_Query::query() for information on accepted arguments.
+			 *
+			 * @param array $comment_args An array of arguments used to retrieve the recent comments.
+			 * @param array $instance     Array of settings for the current widget.
+			 */
 			apply_filters(
 				'widget_comments_args',
 				array(
@@ -112,7 +121,22 @@
 			$output .= $args['before_title'] . $title . $args['after_title'];
 		}
 
-		$output .= '<ul id="recentcomments">';
+		$recent_comments_id = ( $first_instance ) ? 'recentcomments' : "recentcomments-{$this->number}";
+		$first_instance     = false;
+
+		$format = current_theme_supports( 'html5', 'navigation-widgets' ) ? 'html5' : 'xhtml';
+
+		/** This filter is documented in wp-includes/widgets/class-wp-nav-menu-widget.php */
+		$format = apply_filters( 'navigation_widgets_format', $format );
+
+		if ( 'html5' === $format ) {
+			// The title may be filtered: Strip out HTML and make sure the aria-label is never empty.
+			$title      = trim( strip_tags( $title ) );
+			$aria_label = $title ? $title : $default_title;
+			$output    .= '<nav role="navigation" aria-label="' . esc_attr( $aria_label ) . '">';
+		}
+
+		$output .= '<ul id="' . esc_attr( $recent_comments_id ) . '">';
 		if ( is_array( $comments ) && $comments ) {
 			// Prime cache for associated posts. (Prime post term cache if we need it for permalinks.)
 			$post_ids = array_unique( wp_list_pluck( $comments, 'comment_post_ID' ) );
@@ -120,8 +144,8 @@
 
 			foreach ( (array) $comments as $comment ) {
 				$output .= '<li class="recentcomments">';
-				/* translators: comments widget: 1: comment author, 2: post link */
 				$output .= sprintf(
+					/* translators: Comments widget. 1: Comment author, 2: Post link. */
 					_x( '%1$s on %2$s', 'widgets' ),
 					'<span class="comment-author-link">' . get_comment_author_link( $comment ) . '</span>',
 					'<a href="' . esc_url( get_comment_link( $comment ) ) . '">' . get_the_title( $comment->comment_post_ID ) . '</a>'
@@ -130,6 +154,11 @@
 			}
 		}
 		$output .= '</ul>';
+
+		if ( 'html5' === $format ) {
+			$output .= '</nav>';
+		}
+
 		$output .= $args['after_widget'];
 
 		echo $output;
@@ -163,11 +192,15 @@
 		$title  = isset( $instance['title'] ) ? $instance['title'] : '';
 		$number = isset( $instance['number'] ) ? absint( $instance['number'] ) : 5;
 		?>
-		<p><label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
-		<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" /></p>
+		<p>
+			<label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label>
+			<input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
+		</p>
 
-		<p><label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of comments to show:' ); ?></label>
-		<input class="tiny-text" id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" /></p>
+		<p>
+			<label for="<?php echo $this->get_field_id( 'number' ); ?>"><?php _e( 'Number of comments to show:' ); ?></label>
+			<input class="tiny-text" id="<?php echo $this->get_field_id( 'number' ); ?>" name="<?php echo $this->get_field_name( 'number' ); ?>" type="number" step="1" min="1" value="<?php echo $number; ?>" size="3" />
+		</p>
 		<?php
 	}