private function subCompile(&$activeConfig, $lineConfig)
    {
        if (preg_match($this->startMultiLine, $lineConfig, $container)) {
            return $this->findEndingKey(trim($container['key']), trim($container['value']), $activeConfig);
        }

        if (!preg_match($this->simpleDirective, $lineConfig, $container)) {
            throw InvalidConfigException::forSimpleDirectiveSyntaxError($lineConfig);
        }

        return $this->buildSimpleDirective(trim($container['key']), trim($container['value']));
    }