It is certainly documented <https://nim-lang.org/docs/destructors.html#the-cursor-pragma>
There is no copying in the above code. As can be seen by the pointers. > Obviously, with literals and expressions the string does not exist on the > stack so copying is necessary Strings never exist on the stack they're always a `(ptr StringData, len)` even in the case they point to a COW literal. So I'm uncertain what you think you're avoiding.
