Is there a list of what JavaScript works in magazines?

I'm surprised to see a magazine can inject custom JavaScript at all - it seems neat, but also if left unmanaged it could be a disaster waiting to happen (session hijacking, putting ads into feeds, crypto mining, etc.).

I just tried adding alert('Hello world!'); to the JavaScript section of my test magazine and nothing happened, though - which leads me to believe there may be some allowlist of what JavaScript is and isn't okay.

Is that documented anywhere?