* Global variables still exist and can be stored to / loaded from by any code

* Only convention stops a function from constructing its own `Io`

* Only convention stops a function from reaching directly into low-level primitives (e.g. syscalls or libc FFI)

However, in practice, we've found that such conventions tend to be fairly well-respected in most Zig code. I anticipate `Io` being no different. So, if you see a function which doesn't take `Io`, you can be pretty confident (particularly if it's in a somewhat reputable codebase!) that it's not interacting with the system (e.g. doing filesystem accesses, opening sockets, sleeping the thread).