Help understanding PHP Post With ESP32 and Client

I am following code from here to be able to post images to the web, and I was wondering how I could use the client library to just send text. Within Rui Santos’ code he has the line:

String head = "--RandomNerdTutorials\r\nContent-Disposition: form-data; name=\"imageFile\"; filename=\"esp32-cam.jpg\"\r\nContent-Type: image/jpeg\r\n\r\n";

I was wondering how it was that he wrote the code in this specific format (what PHP reference did he use), as well as how I may be able to manipulate it in order to send something like a struct, or even just a string.