Those where the rules I was referring to. In this case `x` is a function call, it is `.noSideEffect` (after the echo was removed) and has one argument, let's call it `y` here instead of reusing `x` like the RFC.
`y` is not isolated as it is a ref type stored in a variable, but looking at the _or_ clause `f`'s return type cannot alias `y`'s type. This lead me to believe that it should indeed be considered isolateable. I'm not sure where variables factor into this, as the return type can't alias the variable anyways.
