register_setting()

function register_setting( $option_group, $option_name, $args = array() ) {
	global $new_allowed_options, $gc_registered_settings;

	/*
	 * In 5.5.0, the `$new_whitelist_options` global variable was renamed to `$new_allowed_options`.
	 * Please consider writing more inclusive code.
	 */
	$GLOBALS['new_whitelist_options'] = &$new_allowed_options;

	$defaults = array(
		'type'              => 'string',
		'group'             => $option_group,
		'description'       => '',
		'sanitize_callback' => null,
		'show_in_rest'      => false,
	);

	// Back-compat: old sanitize callback is added.
	if ( is_callable( $args ) ) {
		$args = array(
			'sanitize_callback' => $args,
		);
	}

	/**
	 * Filters the registration arguments when registering a setting.
	 *
	 * @since 4.7.0
	 *
	 * @param array  $args         Array of setting registration arguments.
	 * @param array  $defaults     Array of default arguments.
	 * @param string $option_group Setting group.
	 * @param string $option_name  Setting name.
	 */
	$args = apply_filters( 'register_setting_args', $args, $defaults, $option_group, $option_name );

	$args = gc_parse_args( $args, $defaults );

	// Require an item schema when registering settings with an array type.
	if ( false !== $args['show_in_rest'] && 'array' === $args['type'] && ( ! is_array( $args['show_in_rest'] ) || ! isset( $args['show_in_rest']['schema']['items'] ) ) ) {
		_doing_it_wrong( __FUNCTION__, __( 'When registering an "array" setting to show in the REST API, you must specify the schema for each array item in "show_in_rest.schema.items".' ), '5.4.0' );
	}

	if ( ! is_array( $gc_registered_settings ) ) {
		$gc_registered_settings = array();
	}

	if ( 'misc' === $option_group ) {
		_deprecated_argument(
			__FUNCTION__,
			'3.0.0',
			sprintf(
				/* translators: %s: misc */
				__( 'The "%s" options group has been removed. Use another settings group.' ),
				'misc'
			)
		);
		$option_group = 'general';
	}

	if ( 'privacy' === $option_group ) {
		_deprecated_argument(
			__FUNCTION__,
			'3.5.0',
			sprintf(
				/* translators: %s: privacy */
				__( 'The "%s" options group has been removed. Use another settings group.' ),
				'privacy'
			)
		);
		$option_group = 'reading';
	}

	$new_allowed_options[ $option_group ][] = $option_name;

	if ( ! empty( $args['sanitize_callback'] ) ) {
		add_filter( "sanitize_option_{$option_name}", $args['sanitize_callback'] );
	}
	if ( array_key_exists( 'default', $args ) ) {
		add_filter( "default_option_{$option_name}", 'filter_default_option', 10, 3 );
	}

	/**
	 * Fires immediately before the setting is registered but after its filters are in place.
	 *
	 * @since 5.5.0
	 *
	 * @param string $option_group Setting group.
	 * @param string $option_name  Setting name.
	 * @param array  $args         Array of setting registration arguments.
	 */
	do_action( 'register_setting', $option_group, $option_name, $args );

	$gc_registered_settings[ $option_name ] = $args;
}

add_action( 'admin_init',    'foo_register_settings' );
add_action( 'rest_api_init', 'foo_register_settings' );

function foo_register_settings() {
	register_setting(
		'foo',
		'foo_my_setting',
		array(
			'type'              => 'string',
			'show_in_rest'      => true,
			'sanitize_callback' => 'sanitize_text_field',
		)
	);
}

const	PLUGIN_SLUG =	'MyPlugin';

/*
 *	Setup Plug-In Hooks (Namespaced Example)
 */
add_action( 'gc_loaded', __NAMESPACE__.'on_gc_loaded' );

if ( is_blog_admin() ) {
	register_activation_hook( __FILE__,  __NAMESPACE__.'on_activate' );
	register_deactivation_hook( __FILE__,  __NAMESPACE__.'on_deactivate' );
	
	add_action( 'admin_menu', __NAMESPACE__.'on_admin_menu' );
	add_action( 'admin_init', __NAMESPACE__.'on_admin_init' );
	add_filter( 'plugin_action_links_' . plugin_basename( __FILE__ ), __NAMESPACE__.'action_links' );
}
return;

/*
 *	Add custom options to whitelist, allowing valiated settings to be saved by form.
 */
function on_admin_init(): void 
{
	register_setting( PLUGIN_SLUG, PLUGIN_SLUG, [ 'sanitize_callback' => __NAMESPACE__.'sanitize_settings' ] ); 
}

/*
 *	Sanitize the form input.
 */
function sanitize_settings( $input = NULL ):  
{
	// Detect multiple sanitizing passes.
	// Accomodates bug: https://core.trac.gechiui.org/ticket/21989
	static $pass_count = 0; $pass_count++;

	if ( $pass_count <= 1 ) {
		// Handle any single-time / performane sensitive actions.

	}

	// Insert regular santizing code here.
}

add_action( 'admin_init',    'gcdocs_foo_register_settings' );
add_action( 'rest_api_init', 'gcdocs_foo_register_settings' );
function gcdocs_foo_register_settings() {
	register_setting( 'general_setting', 'id' );
	register_setting( 'general_setting', 'order' );
	register_setting(
		'general_setting',
		'slider-data',
		array(
			'show_in_rest' => array(
				'name' => 'images_slide',
				'schema' => array(
					'type'  => 'array',
					'items' => array(
						'id'    => 'string',
						'order' => 'string',
					),
				),
			),
			'type' => 'array',
			'sanitize_callback' => array( $this, 'gcdocs_admin_post_save_data' ),
		)
	);
}

register_setting(
	'dp_example_settings_group',
	'dp_example_array_settings',
	array(
		'type'         => 'object',
		'default'      => array(
			'A',
			'B',
			'C',
		),
		'show_in_rest' => array(
			'schema' => array(
				'type'  => 'object',
				'items' => array(
					'type' => 'string',
				),
			),
		),
	)
);

register_setting(
	'dp_example_settings_group',
	'dp_example_object_settings',
	array(
		'type'         => 'object',
		'default'      => array(
			'some_str' => 'A',
			'some_int' => 3,
		),
		'show_in_rest' => array(
			'schema' => array(
				'type'       => 'object',
				'properties' => array(
					'some_str' => array(
						'type' => 'string',
					),
					'some_int' => array(
						'type' => 'integer',
					),
				),
			),
		),
	)
);