I think this was the reason I invented the whole thing.
> The only slightly awkward changes are: * we now have to use `apply(&())` in this case * when giving a callback to such a builder we have to use `|_: &_|` now, but this was also the case for any closure that got converted into a `RenderFn`.
Being forced to use |_: &_| is ugly, and the compiler errors for that are even more ugly and confusing. So I am not sure about this change.