https://www.php.net/manual/de/solrinputdocument.haschilddocuments.php
PHP: SolrInputDocument::hasChildDocuments - Manual
Returns true if the document has any child documents
phpmanual
https://www.php.net/manual/it/solrdocument.haschilddocuments.php
PHP: SolrDocument::hasChildDocuments - Manual
Checks whether the document has any child documents
phpmanual