syntax_data: {"ast_node_type":"other","tokens":[{"end":83,"kind":"keyword","start":0,"text":"///"}]}
source_snippet:     /// be used over [expand_free_alias_tys] as an optimization in situations where
context_before:     /// This only expands free alias types in “head” / outermost positions. It can
context_after:     /// one only really cares about the *kind* of the final aliased type but not