3.6 Locations: #%variable-reference
When (#%top . id) is used, then the variable reference refers to the same variable as (#%top . id). Note that (#%top . id) is not allowed if id is locally bound or within a module if id is bound as a transformer.
A variable reference can be used with variable-reference->empty-namespace, variable-reference->resolved-module-path, and variable-reference->namespace, but facilities like define-namespace-anchor and namespace-anchor->namespace wrap those to provide a clearer interface. A variable reference is also useful to low-level extensions; see Inside: Racket C API.