syntax_data: {"ast_node_type":"other","tokens":[{"end":30,"kind":"keyword","start":0,"text":"//!"}]}
source_snippet: //!   other types of interest.
context_before: //!   impl, because some of the types of interest are recursive and can contain
context_after: //! - A `TypeFolder`/`FallibleTypeFolder` may also call into a `TypeSuperFoldable`