I can't find unregisterBeforeRender and onReadyObservable document,can you show me some demo?

Questions
1

when i do something in registerBeforeRender（myfunction） ，after that i want to stop this registerBeforeRender ，how to use the unregisterBeforeRender ？

I don’t know onReadyObservable When to use,can you show me some demo?

2

Hi!
https://doc.babylonjs.com/playground/?code=unregisterBeforeRender