Question Is Unity XR = SteamVR ?

I wan't to make a VR Game that should use SteamVR and support all VR Headsets like Oculus, Vive, Valve Index and Windows Mixed Reality...
But what exactley is Unity XR ? Is it the other part to interact with Steam VR or is it somthing different?
Do I even need Unity XR If I want to use SteamVR?

 

As far as I know SteamVR is pretty much just a VR version of the Steam desktop application. I.e. it's a VR hub for you to launch the VR games in your Steam library from. It doesn't have anything to do with Unity XR or any other XR/VR framework.

Information about supported hardware platforms etc.. are here:
https://docs.unity3d.com/Manual/XR.html

More info about SteamVR:
https://store.steampowered.com/app/250820/SteamVR/

 

If I use this plugin right here: https://assetstore.unity.com/packages/tools/integration/steamvr-plugin-32647
Do it will support by itself: "Oculus, Vive, and Windows Mixed Realty? Or do I need Unity XR for it also?