syntax_data: {"ast_node_type":"function","tokens":[{"end":71,"kind":"keyword","start":0,"text":"fn"}]}
source_snippet:     fn prefill(init: &[&'static str], extra: &[&'static str]) -> Self {
context_before:     // `ByteSymbol`.
context_after:         let byte_strs = FxIndexSet::from_iter(