ESP32- SPI- SPI.h functions

Hello.

I want to set up ESP32' SPI as an slave so that it always listens to the master and wait for probable incoming messages. in an provided example in IDE, hspi->transfer() function is used.
I could not find corresponding explanations for this function on web. where should I find the implementation of this function , explanations about it or the SPI.c or SPI.C++ library?

I checked the usual paths in my computer (docs, user/arduino) but I could not find such I file like SPI.c

thanks in advance

I've used the ESP32 SPI Master Driver with great success. Perhaps you'll have good luck using the SPI Slave Driver - ESP32 - — ESP-IDF Programming Guide latest documentation (espressif.com)