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

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?

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