syntax_data: {"ast_node_type":"other","tokens":[{"end":84,"kind":"keyword","start":0,"text":"Option<ty::DebruijnIndex>,"}]}
source_snippet:         Option<ty::DebruijnIndex>, // Debruijn index of the folded late-bound region
context_before:                 dyn FnMut(
context_after:         ty::DebruijnIndex,         // Index corresponding to binder level