syntax_data: {"ast_node_type":"other","tokens":[{"end":35,"kind":"keyword","start":0,"text":"a_region:"}]}
source_snippet:         a_region: ty::Region<'tcx>,
context_before:         b_data: &'tcx ty::List<ty::PolyExistentialPredicate<'tcx>>,
context_after:         b_region: ty::Region<'tcx>,