syntax_data: {"ast_node_type":"other","tokens":[{"end":29,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:                 // character.
context_before:                 // We should never see a byte position in the middle of a
context_after:                 assert!(bpos.to_u32() >= mbc.pos.to_u32() + mbc.bytes as u32);