[devit]

The more idiomatic way would be to return an Rc<RefCell<Element>>.

Accessing it will indeed panic if someone else has an active mutable reference to the contents of the refcell, but the idea is that you should only keep that for the section of code that actually modifies the object.

The reason this feature exists is that it prevents code observing partially modified objects that could be temporarily missing required invariants (in addition to preventing mutating object with references to parts of them which can result in dangling pointers and thus memory unsafety).

You can also use Cell as the parent argues with the benefit of never failing, but then you don't get protection from recursive calls exposing violated invariants and you need to change the implementation of Element itself.