What is the most up to date Plutus documentation?

I am a research student looking to do some work centred around Plutus State Machines, but in order to start I need to make sure I have the most accurate documentation.

I have found this one, which contains somewhere down the list a Plutus.Contract.StateMachine documentation. Optimally, I would have linked it, but apparently there is a limit of 2 links per post.

I think and hope that the above one is the correct one, but I also subsequently found this documentation, which is subtly different. Consequently, I wanted to ask and see if someone can direct me to the precise location of what is most recent and accurate.

Thank you in advance for your help!