syntax_data: {"ast_node_type":"other","tokens":[{"end":73,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:         // - For dummy symbols that are never used and absolutely must be
context_before:         //   `Option<Symbol>` when "no symbol" is a possibility.
context_after:         //   present, it's better to use `sym::dummy` than `sym::empty`, because