https://www.php.net/manual/tr/solrinputdocument.getfieldnames.php
PHP: SolrInputDocument::getFieldNames - Manual
Returns an array containing all the fields in the document
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https://learn.microsoft.com/ko-kr/windows/win32/api/oaidl/nf-oaidl-irecordinfo-getfieldnames
IRecordInfo::GetFieldNames(oaidl.h) - Win32 apps | Microsoft Learn
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