Pointee not on the heap?

True! I guess the precise way of saying what's going on with Pointee is "it can't be used in any place that requires Rust code to have knowledge of its size, meaning that it can only be stored as the last element of (heap-allocated) Rust structures and must always be interacted with via a pointer of some kind, even if that is a fake 'pointer' invented by C code", but that doesn't really fit in the little summary table. So given the surrounding article for context, I'm comfortable summarizing those rules as "not on the stack". :)