什么是WordPress小部件函数中的实例？

function custom_widgets_init() {
    register_sidebar( array(
        'name'          => 'Custom Sidebar',
        'id'            => 'custom-sidebar',
        'description'   => 'Add widgets here to appear in the custom sidebar.',
        'before_widget' => '<div class="widget">',
        'after_widget'  => '</div>',
        'before_title'  => '<h2 class="widget-title">',
        'after_title'   => '</h2>',
    ) );
}
add_action( 'widgets_init', 'custom_widgets_init' );

<div id="sidebar" class="sidebar">
    <?php dynamic_sidebar( 'custom-sidebar' ); ?>
</div>