syntax_data: {"ast_node_type":"other","tokens":[{"end":49,"kind":"keyword","start":0,"text":"assert!((2..=4).contains(&char_len));"}]}
source_snippet:             assert!((2..=4).contains(&char_len));
context_before:             let pos = RelativeBytePos::from_usize(i) + output_offset;
context_after:             let mbc = MultiByteChar { pos, bytes: char_len as u8 };