syntax_data: {"ast_node_type":"function","tokens":[{"end":45,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn decode(d: &mut D) -> RelativeBytePos {
context_before: impl<D: Decoder> Decodable<D> for RelativeBytePos {
context_after:         RelativeBytePos(d.read_u32())