Source

File: wp-includes/class-wp-customize-manager.php

public function add_dynamic_settings( $setting_ids ) {
		$new_settings = array();
		foreach ( $setting_ids as $setting_id ) {
			// Skip settings already created.
			if ( $this->get_setting( $setting_id ) ) {
				continue;
			}

			$setting_args  = false;
			$setting_class = 'WP_Customize_Setting';

			/**
			 * Filters a dynamic setting's constructor args.
			 *
			 * For a dynamic setting to be registered, this filter must be employed
			 * to override the default false value with an array of args to pass to
			 * the WP_Customize_Setting constructor.
			 *
			 * @since 4.2.0
			 *
			 * @param false|array $setting_args The arguments to the WP_Customize_Setting constructor.
			 * @param string      $setting_id   ID for dynamic setting, usually coming from `$_POST['customized']`.
			 */
			$setting_args = apply_filters( 'customize_dynamic_setting_args', $setting_args, $setting_id );
			if ( false === $setting_args ) {
				continue;
			}

			/**
			 * Allow non-statically created settings to be constructed with custom WP_Customize_Setting subclass.
			 *
			 * @since 4.2.0
			 *
			 * @param string $setting_class WP_Customize_Setting or a subclass.
			 * @param string $setting_id    ID for dynamic setting, usually coming from `$_POST['customized']`.
			 * @param array  $setting_args  WP_Customize_Setting or a subclass.
			 */
			$setting_class = apply_filters( 'customize_dynamic_setting_class', $setting_class, $setting_id, $setting_args );

			$setting = new $setting_class( $this, $setting_id, $setting_args );

			$this->add_setting( $setting );
			$new_settings[] = $setting;
		}
		return $new_settings;
	}