Minecraft Forge 1.8.9 Modding Documentation?

I'm currently trying to program mods for Minecraft 1.8.9 in Java. I found a couple of good tutorials that go through the basics. However, I can't find any documentation on Forge 1.8.9. On the official Forge site you can only find documentation for 1.15 and 1.16. Surely there has to be something to it somewhere?

The last one I found is the one for 1.12:

https://github.com/...ree/1.12.x

I have no idea how to program mods but if you want to download mods then take a look at the Twitch app. Because I always get the mods. Maybe you can do your mod there too.