+ // Now we figure out which item grants our parent (`derived_from`) permission.
+ // We use that to determine (a) where to put the new item, and for raw pointers
+ // (b) whether to given read-only or read-write access.
+ // FIXME: This handling of raw pointers is fragile, very fragile. What if we do
+ // not get "the right one", like when there are multiple items granting `derived_from`
+ // and we accidentally create a read-only pointer? This can happen for two-phase borrows
+ // (then there's a `Unique` and a `SharedReadOnly` for the same tag), and for raw pointers
+ // (which currently all are `Untagged`).