syntax_data: {"ast_node_type":"other","tokens":[{"end":78,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// For example, if the coroutine returned by the closure borrows `String`
context_before:     ///
context_after:     /// from the closure's upvars, this will be `for<'env> fn() -> (&'env String,)`,