syntax_data: {"ast_node_type":"other","tokens":[{"end":22,"kind":"keyword","start":0,"text":"///"}]}
source_snippet: ///   specified above.
context_before: ///   implements `CK<(u32, u32), Output = u32>`, where `CK` is the trait
context_after: /// - U is a type parameter representing the types of its upvars, tupled up