diff -r 3d4e9c994f10 -r a86126ab1dd4 wp/wp-includes/widgets/class-wp-widget-categories.php
--- a/wp/wp-includes/widgets/class-wp-widget-categories.php	Tue Oct 22 16:11:46 2019 +0200
+++ b/wp/wp-includes/widgets/class-wp-widget-categories.php	Tue Dec 15 13:49:49 2020 +0100
@@ -34,8 +34,8 @@
 	 * Outputs the content for the current Categories widget instance.
 	 *
 	 * @since 2.8.0
-	 *
-	 * @staticvar bool $first_dropdown
+	 * @since 4.2.0 Creates a unique HTML ID for the `<select>` 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'.
@@ -44,14 +44,15 @@
 	public function widget( $args, $instance ) {
 		static $first_dropdown = true;
 
-		$title = ! empty( $instance['title'] ) ? $instance['title'] : __( 'Categories' );
+		$default_title = __( 'Categories' );
+		$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 );
 
-		$c = ! empty( $instance['count'] ) ? '1' : '0';
-		$h = ! empty( $instance['hierarchical'] ) ? '1' : '0';
-		$d = ! empty( $instance['dropdown'] ) ? '1' : '0';
+		$count        = ! empty( $instance['count'] ) ? '1' : '0';
+		$hierarchical = ! empty( $instance['hierarchical'] ) ? '1' : '0';
+		$dropdown     = ! empty( $instance['dropdown'] ) ? '1' : '0';
 
 		echo $args['before_widget'];
 
@@ -61,12 +62,12 @@
 
 		$cat_args = array(
 			'orderby'      => 'name',
-			'show_count'   => $c,
-			'hierarchical' => $h,
+			'show_count'   => $count,
+			'hierarchical' => $hierarchical,
 		);
 
-		if ( $d ) {
-			echo sprintf( '<form action="%s" method="get">', esc_url( home_url() ) );
+		if ( $dropdown ) {
+			printf( '<form action="%s" method="get">', esc_url( home_url() ) );
 			$dropdown_id    = ( $first_dropdown ) ? 'cat' : "{$this->id_base}-dropdown-{$this->number}";
 			$first_dropdown = false;
 
@@ -89,9 +90,11 @@
 			wp_dropdown_categories( apply_filters( 'widget_categories_dropdown_args', $cat_args, $instance ) );
 
 			echo '</form>';
+
+			$type_attr = current_theme_supports( 'html5', 'script' ) ? '' : ' type="text/javascript"';
 			?>
 
-<script type='text/javascript'>
+<script<?php echo $type_attr; ?>>
 /* <![CDATA[ */
 (function() {
 	var dropdown = document.getElementById( "<?php echo esc_js( $dropdown_id ); ?>" );
@@ -107,24 +110,40 @@
 
 			<?php
 		} else {
+			$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;
+				echo '<nav role="navigation" aria-label="' . esc_attr( $aria_label ) . '">';
+			}
 			?>
-		<ul>
-			<?php
-			$cat_args['title_li'] = '';
+
+			<ul>
+				<?php
+				$cat_args['title_li'] = '';
 
-			/**
-			 * Filters the arguments for the Categories widget.
-			 *
-			 * @since 2.8.0
-			 * @since 4.9.0 Added the `$instance` parameter.
-			 *
-			 * @param array $cat_args An array of Categories widget options.
-			 * @param array $instance Array of settings for the current widget.
-			 */
-			wp_list_categories( apply_filters( 'widget_categories_args', $cat_args, $instance ) );
-			?>
-		</ul>
+				/**
+				 * Filters the arguments for the Categories widget.
+				 *
+				 * @since 2.8.0
+				 * @since 4.9.0 Added the `$instance` parameter.
+				 *
+				 * @param array $cat_args An array of Categories widget options.
+				 * @param array $instance Array of settings for the current widget.
+				 */
+				wp_list_categories( apply_filters( 'widget_categories_args', $cat_args, $instance ) );
+				?>
+			</ul>
+
 			<?php
+			if ( 'html5' === $format ) {
+				echo '</nav>';
+			}
 		}
 
 		echo $args['after_widget'];
@@ -158,23 +177,29 @@
 	 * @param array $instance Current settings.
 	 */
 	public function form( $instance ) {
-		//Defaults
+		// Defaults.
 		$instance     = wp_parse_args( (array) $instance, array( 'title' => '' ) );
 		$count        = isset( $instance['count'] ) ? (bool) $instance['count'] : false;
 		$hierarchical = isset( $instance['hierarchical'] ) ? (bool) $instance['hierarchical'] : false;
 		$dropdown     = isset( $instance['dropdown'] ) ? (bool) $instance['dropdown'] : false;
 		?>
-		<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( $instance['title'] ); ?>" /></p>
-
-		<p><input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'dropdown' ); ?>" name="<?php echo $this->get_field_name( 'dropdown' ); ?>"<?php checked( $dropdown ); ?> />
-		<label for="<?php echo $this->get_field_id( 'dropdown' ); ?>"><?php _e( 'Display as dropdown' ); ?></label><br />
+		<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( $instance['title'] ); ?>" />
+		</p>
 
-		<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'count' ); ?>" name="<?php echo $this->get_field_name( 'count' ); ?>"<?php checked( $count ); ?> />
-		<label for="<?php echo $this->get_field_id( 'count' ); ?>"><?php _e( 'Show post counts' ); ?></label><br />
+		<p>
+			<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'dropdown' ); ?>" name="<?php echo $this->get_field_name( 'dropdown' ); ?>"<?php checked( $dropdown ); ?> />
+			<label for="<?php echo $this->get_field_id( 'dropdown' ); ?>"><?php _e( 'Display as dropdown' ); ?></label>
+			<br />
 
-		<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'hierarchical' ); ?>" name="<?php echo $this->get_field_name( 'hierarchical' ); ?>"<?php checked( $hierarchical ); ?> />
-		<label for="<?php echo $this->get_field_id( 'hierarchical' ); ?>"><?php _e( 'Show hierarchy' ); ?></label></p>
+			<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'count' ); ?>" name="<?php echo $this->get_field_name( 'count' ); ?>"<?php checked( $count ); ?> />
+			<label for="<?php echo $this->get_field_id( 'count' ); ?>"><?php _e( 'Show post counts' ); ?></label>
+			<br />
+
+			<input type="checkbox" class="checkbox" id="<?php echo $this->get_field_id( 'hierarchical' ); ?>" name="<?php echo $this->get_field_name( 'hierarchical' ); ?>"<?php checked( $hierarchical ); ?> />
+			<label for="<?php echo $this->get_field_id( 'hierarchical' ); ?>"><?php _e( 'Show hierarchy' ); ?></label>
+		</p>
 		<?php
 	}