{"ast_node_type":"other","tokens":[{"end":65,"kind":"keyword","start":0,"text":"Fn(FnCtxt,"}]}
            Fn(FnCtxt, &'a $($mut)? Visibility, &'a $($mut)? Fn),
            /// E.g., `fn foo()`, `fn foo(&self)`, or `extern "Abi" fn foo()`.