register_sidebar() WordPress Function

function register_sidebar( $args = array() ) {
	global $wp_registered_sidebars;

	$i = count( $wp_registered_sidebars ) + 1;

	$id_is_empty = empty( $args['id'] );

	$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",
		'before_sidebar' => '',
		'after_sidebar'  => '',
		'show_in_rest'   => false,
	);

	/**
	 * Filters the sidebar default arguments.
	 *
	 * @since 5.3.0
	 *
	 * @see register_sidebar()
	 *
	 * @param array $defaults The default sidebar arguments.
	 */
	$sidebar = wp_parse_args( $args, apply_filters( 'register_sidebar_defaults', $defaults ) );

	if ( $id_is_empty ) {
		_doing_it_wrong(
			__FUNCTION__,
			sprintf(
				/* translators: 1: The 'id' argument, 2: Sidebar name, 3: Recommended 'id' value. */
				__( 'No %1$s was set in the arguments array for the "%2$s" sidebar. Defaulting to "%3$s". Manually set the %1$s to "%3$s" to silence this notice and keep existing sidebar content.' ),
				'<code>id</code>',
				$sidebar['name'],
				$sidebar['id']
			),
			'4.2.0'
		);
	}

	$wp_registered_sidebars[ $sidebar['id'] ] = $sidebar;

	add_theme_support( 'widgets' );

	/**
	 * Fires once a sidebar has been registered.
	 *
	 * @since 3.0.0
	 *
	 * @param array $sidebar Parsed arguments for the registered sidebar.
	 */
	do_action( 'register_sidebar', $sidebar );

	return $sidebar['id'];
}