Where can i find documentation on URLRequest default header?

Question

From the Internet I read that URLRequest sends an "Accept-Encoding" header by default. I also read that URLSession auto decompresses any data that’s returned compressed. However this information is what an internet post says. I want to read this information in the official Apple docs. I visit the docs and read about URLSession & URLRequest. However I can’t find where it says, to confirm what I read on the internet, that it does send the "Accept-Encoding" headers by default or that it auto decompresses compressed data. I know it does the latter as I am able to parse compressed data and have to do nothing to decompress. Just tell me where this stuff is documented by Apple so I can read about it. Thanks