Direct link: https://jprzywoski.github.io/sdl-docs/
This is a mirror of various reference guides and code samples related to SDL 1.2.
During the transition from SDL to SDL 2 around 2013-14 the official website had the links and resources related to SDL 1.2 removed.
Luckily web archive preserved most of it - https://web.archive.org/web/20110706072630/http://www.libsdl.org/
I am not affiliated with SDL project in any way, this is completely unofficial, and originally was just for my own personal use.