I tried to look at the main documentation at http://graphics.pixar.com/usd/docs/index.html and http://graphics.pixar.com/usd/docs/Usdz-File-Format-Specification.html but cou
You can now easily create/export USDZ from Unity:
https://blogs.unity3d.com/2019/03/28/pixars-universal-scene-description-for-unity-out-in-preview/