register_sidebar()　WordPress関数　

<?php

$args = array(
	'name'          => __( 'Sidebar name', 'theme_text_domain' ),
	'id'            => 'unique-sidebar-id',
	'description'   => '',
	'class'         => '',
	'before_widget' => '<li id="%1$s" class="widget %2$s">',
	'after_widget'  => '</li>',
	'before_title'  => '<h2 class="widgettitle">',
	'after_title'   => '</h2>' ); 

?>

<?php

function nawate_widgets_init(){

// ウィジェット機能を追加。

register_sidebar( array(
    'name' => 'フッターバーウィジェットエリア01',
    'id' => 'subcol-widget-footer-area01',
    'description' => 'サイドバーのウィジェットエリア',
    'before_widget' => '<aside id="%1$s" class="widget %2$s">',
    'after_widget' => '</aside>',
    'before_title' => '<h2 class="widget__title font-serif">',
    'after_title' => '</h2>',
  ) );

add_action('widgets_init','nawate_widgets_init');

?>

<?php
/**
 * Builds the definition for a single sidebar and returns the ID.
 *
 * Accepts either a string or an array and then parses that against a set
 * of default arguments for the new sidebar. WordPress will automatically
 * generate a sidebar ID and name based on the current number of registered
 * sidebars if those arguments are not included.
 *
 * When allowing for automatic generation of the name and ID parameters, keep
 * in mind that the incrementor for your sidebar can change over time depending
 * on what other plugins and themes are installed.
 *
 * If theme support for 'widgets' has not yet been added when this function is
 * called, it will be automatically enabled through the use of add_theme_support()
 *
 * @since 2.2.0
 *
 * @global array $wp_registered_sidebars Stores the new sidebar in this array by sidebar ID.
 *
 * @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.
 * }
 * @return string Sidebar ID added to $wp_registered_sidebars global.
 */
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",
	);

	/**
	 * 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'];
}
?>