What is the difference of issacgym and omniissacgym?

Hi, I am currently preparing to use isaacGym to build my RL environment, but I have found two versions of isaacGym. The introduction states that Omni isaac Gym is the latest, but I found that there is not much explanation for Omni isaac Gym. On the contrary, isaac Gym has its own docs:
About Isaac Gym — Isaac Gym documentation (junxnone.github.io)

Does omni isaac gym has the docs like this? Where can I find the API that used in omni isaac gym?

@Robo_qq this thread seem relevant - Differences Between IsaacGymEnvs and OmniIsaacGymEnvs? - #3 by piperunner.in

Thanks. And where can I find the docs like this?
About Isaac Gym — Isaac Gym documentation (junxnone.github.io)

Or is the omniisaacgym use the Isaac sim API?

perhaps this is what you are looking for? GitHub - NVIDIA-Omniverse/OmniIsaacGymEnvs: Reinforcement Learning Environments for Omniverse Isaac Gym

the doc may also help - 9.1. Overview & Getting Started — Omniverse IsaacSim latest documentation (nvidia.com)