What is "stable staging"?

What is the “stable staging” ?
Another intermediate branch between testing and stable ?

Staging branch is for testing final stable branch repo snapshot, after all packages from testing are got together and there is a concern that everything installed at once can break something, the snapshot have test on Stable Staging branch.

Not sure if snapshot is a proper term here, but in general it works that way.

Thank you for your answer !

no ! stable-staging : packages go from unstable and not only testing , it’s for dev only

Ok, so just by curiosity why is there no testing-staging ?