PartKeepr\ExportBundle\DependencyInjection\Compiler\XmlExcelFormatPass::process PHP Method

    public function process(ContainerBuilder $container)
    {
        $container->getDefinition('api.format_negotiator')->addMethodCall('registerFormat', ['xlsx', ['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'], true]);
    }