diff --git a/wp-includes/version.php b/wp-includes/version.php
index 487ee1834c..3b16e561f2 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.6-alpha-49202';
+$wp_version = '5.6-alpha-49203';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-includes/widgets.php b/wp-includes/widgets.php
index 0d176687fb..a7f54d697b 100644
--- a/wp-includes/widgets.php
+++ b/wp-includes/widgets.php
@@ -219,28 +219,35 @@ function register_sidebars( $number = 1, $args = array() ) {
  * called, it will be automatically enabled through the use of add_theme_support()
  *
  * @since 2.2.0
+ * @since 5.6.0 Added the `before_sidebar` and `after_sidebar` arguments.
  *
  * @global array $wp_registered_sidebars Registered sidebars.
  *
  * @param array|string $args {
  *     Optional. Array or string of arguments for the sidebar being registered.
  *
- *     @type string $name          The name or title of the sidebar displayed in the Widgets
- *                                 interface. Default 'Sidebar $instance'.
- *     @type string $id            The unique identifier by which the sidebar will be called.
- *                                 Default 'sidebar-$instance'.
- *     @type string $description   Description of the sidebar, displayed in the Widgets interface.
- *                                 Default empty string.
- *     @type string $class         Extra CSS class to assign to the sidebar in the Widgets interface.
- *                                 Default empty.
- *     @type string $before_widget HTML content to prepend to each widget's HTML output when
- *                                 assigned to this sidebar. Default is an opening list item element.
- *     @type string $after_widget  HTML content to append to each widget's HTML output when
- *                                 assigned to this sidebar. Default is a closing list item element.
- *     @type string $before_title  HTML content to prepend to the sidebar title when displayed.
- *                                 Default is an opening h2 element.
- *     @type string $after_title   HTML content to append to the sidebar title when displayed.
- *                                 Default is a closing h2 element.
+ *     @type string $name           The name or title of the sidebar displayed in the Widgets
+ *                                  interface. Default 'Sidebar $instance'.
+ *     @type string $id             The unique identifier by which the sidebar will be called.
+ *                                  Default 'sidebar-$instance'.
+ *     @type string $description    Description of the sidebar, displayed in the Widgets interface.
+ *                                  Default empty string.
+ *     @type string $class          Extra CSS class to assign to the sidebar in the Widgets interface.
+ *                                  Default empty.
+ *     @type string $before_widget  HTML content to prepend to each widget's HTML output when
+ *                                  assigned to this sidebar. Default is an opening list item element.
+ *     @type string $after_widget   HTML content to append to each widget's HTML output when
+ *                                  assigned to this sidebar. Default is a closing list item element.
+ *     @type string $before_title   HTML content to prepend to the sidebar title when displayed.
+ *                                  Default is an opening h2 element.
+ *     @type string $after_title    HTML content to append to the sidebar title when displayed.
+ *                                  Default is a closing h2 element.
+ *     @type string $before_sidebar HTML content to prepend to the sidebar when displayed.
+ *                                  Outputs after the {@see 'dynamic_sidebar_before'} action.
+ *                                  Default empty string.
+ *     @type string $after_sidebar  HTML content to append to the sidebar when displayed.
+ *                                  Outputs before the {@see 'dynamic_sidebar_after'} action.
+ *                                  Default empty string.
  * }
  * @return string Sidebar ID added to $wp_registered_sidebars global.
  */
@@ -253,14 +260,16 @@ function register_sidebar( $args = array() ) {
 
 	$defaults = array(
 		/* translators: %d: Sidebar number. */
-		'name'          => sprintf( __( 'Sidebar %d' ), $i ),
-		'id'            => "sidebar-$i",
-		'description'   => '',
-		'class'         => '',
-		'before_widget' => '<li id="%1$s" class="widget %2$s">',
-		'after_widget'  => "</li>\n",
-		'before_title'  => '<h2 class="widgettitle">',
-		'after_title'   => "</h2>\n",
+		'name'           => sprintf( __( 'Sidebar %d' ), $i ),
+		'id'             => "sidebar-$i",
+		'description'    => '',
+		'class'          => '',
+		'before_widget'  => '<li id="%1$s" class="widget %2$s">',
+		'after_widget'   => "</li>\n",
+		'before_title'   => '<h2 class="widgettitle">',
+		'after_title'    => "</h2>\n",
+		'before_sidebar' => '',
+		'after_sidebar'  => '',
 	);
 
 	/**
@@ -691,6 +700,10 @@ function dynamic_sidebar( $index = 1 ) {
 		return apply_filters( 'dynamic_sidebar_has_widgets', false, $index );
 	}
 
+	$sidebar = $wp_registered_sidebars[ $index ];
+
+	$sidebar['before_sidebar'] = sprintf( $sidebar['before_sidebar'], $sidebar['id'], $sidebar['class'] );
+
 	/**
 	 * Fires before widgets are rendered in a dynamic sidebar.
 	 *
@@ -704,7 +717,10 @@ function dynamic_sidebar( $index = 1 ) {
 	 *                                Default true.
 	 */
 	do_action( 'dynamic_sidebar_before', $index, true );
-	$sidebar = $wp_registered_sidebars[ $index ];
+
+	if ( ! empty( $sidebar['before_sidebar'] ) ) {
+		echo $sidebar['before_sidebar'];
+	}
 
 	$did_one = false;
 	foreach ( (array) $sidebars_widgets[ $index ] as $id ) {
@@ -807,6 +823,10 @@ function dynamic_sidebar( $index = 1 ) {
 		}
 	}
 
+	if ( ! empty( $sidebar['after_sidebar'] ) ) {
+		echo $sidebar['after_sidebar'];
+	}
+
 	/**
 	 * Fires after widgets are rendered in a dynamic sidebar.
 	 *