is_cross_domain example

'selectiveRefresh' => 250,
                'keepAliveSend'    => 1000,
            ),
            'theme'             => array(
                'stylesheet' => $this->get_stylesheet(),
                'active'     => $this->is_theme_active(),
            ),
            'url'               => array(
                'self'          => $self_url,
                'allowed'       => array_map( 'sanitize_url', $this->get_allowed_urls() ),
                'allowedHosts'  => array_unique( $allowed_hosts ),
                'isCrossDomain' => $this->is_cross_domain(),
            ),
            'channel'           => $this->messenger_channel,
            'activePanels'      => array(),
            'activeSections'    => array(),
            'activeControls'    => array(),
            'settingValidities' => $exported_setting_validities,
            'nonce'             => current_user_can( 'customize' ) ? $this->get_nonces() : array(),
            'l10n'              => $l10n,
            '_dirty'            => array_keys( $post_values ),
        );