I was unsafe-reviewing the referencing crate and noticed this:

It's very unclear if this invariant is upheld properly: anchors get threaded through a lot of the code and there are no comments anywhere talking about this

Furthermore, self-referential code is notorious in Rust for being hard to get right: even when the conceptual lifetimes are right there are many subtle things around Rust's aliasing model that you can get wrong.

Some alternate routes:

• Just clone the string
• Use an existing self-referential crate
• See if you can make it work with lifetimes. I'm not convinced this is possible.
• Split out the Anchors map into an AnchorContext type that is not stored within the Registry but instead passed to it, allowing it to reference the registry.