syntax_data: {"ast_node_type":"other","tokens":[{"end":31,"kind":"keyword","start":0,"text":"//!"}]}
source_snippet: //!   other types of interest.)
context_before: //!   excludes `Region` because it is non-recursive, i.e. it never contains
context_after: //! - `TypeFolder`/`FallibleTypeFolder`. One of these is implemented for each