syntax_data: {"ast_node_type":"other","tokens":[{"end":74,"kind":"keyword","start":0,"text":"///"}]}
source_snippet: ///   (sometimes 20+ bits) might occur dozens of times in a typical crate.
context_before: ///   onwards. 15 bits is enough for 99.99%+ of cases, but larger values
context_after: /// - `ctxt_or_parent_or_marker` is 16 bits in `Span` and two 32 bit fields in