syntax_data: {"ast_node_type":"struct","tokens":[{"end":70,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:             // a tuple-struct or tuple-variant. This has the type of a
context_before:             // A reference to something callable -- e.g., a fn, method, or
context_after:             // `Fn` but with the user-given generic parameters.