Request for documentation: Is it safe to mutate contents of `Cell<T>` through `as_ptr`?

Location (URL)

https://doc.rust-lang.org/std/cell/struct.Cell.html#method.as_ptr

Summary

Cell<T>::as_ptr allows you to obtain a pointer to T. This pointer can in theory be used to modify the contents of the cell, but is this sound? If I use ptr::write to write to the value, is that sound? Similarly, if I cast the pointer to &mut T and use that to modify the contents, is that sound (assuming I don't use set or get on the original cell while the mutable reference exists)?

I think answers to these questions should be present in the documentation of Cell<T>::as_ptr, otherwise it is unclear what the returned pointer allows.

Start at the documented Cell::as_ptr entry point linked in the issue, then review the surrounding Cell documentation and the stated pointer-use questions. The documentation work is done when it clearly explains whether ptr::write and casting the pointer to &mut T are sound under the conditions described.