any #rust experts, please help!

in the definition (https://docs.rs/scoped-futures/latest/scoped_futures/type.ScopedBoxFuture.html) of the ScopedBoxFuture it says it's the future which lifetime is upper bounded.

let's say i have something like:

```
conn.transaction::<_, Error, _>(|conn| {
async move {
...
}.scope_boxed()
}).await?;
```
(basically, that's a snippet from the diesel library: https://github.com/weiznich/diesel_async/blob/bf66d1dc05b566ed39f47136109c477c8c58e60e/src/lib.rs#L200-L210)

what would be the upper bound? the surroundings of the conn.transaction itself?