isXmlString example

class XliffFileLoader implements LoaderInterface
{
    public function load(mixed $resource, string $locale, string $domain = 'messages'): MessageCatalogue
    {
        if (!class_exists(XmlUtils::class)) {
            throw new RuntimeException('Loading translations from the Xliff format requires the Symfony Config component.');
        }

        if (!$this->isXmlString($resource)) {
            if (!stream_is_local($resource)) {
                throw new InvalidResourceException(sprintf('This is not a local file "%s".', $resource));
            }

            if (!file_exists($resource)) {
                throw new NotFoundResourceException(sprintf('File "%s" not found.', $resource));
            }

            if (!is_file($resource)) {
                throw new InvalidResourceException(sprintf('This is neither a file nor an XLIFF string "%s".', $resource));
            }
        }