syntax_data: {"ast_node_type":"other","tokens":[{"end":81,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// to return a set of upvars which are borrowed with the given `env_region`.
context_before:     /// When `ClosureKind` is `FnMut`/`Fn`, then this will use the "captures by ref"
context_after:     ///