syntax_data: {"ast_node_type":"function","tokens":[{"end":77,"kind":"keyword","start":0,"text":"pub"}]}
source_snippet:     pub fn lookup_byte_offset(&self, bpos: BytePos) -> SourceFileAndBytePos {
context_before:     /// For a global `BytePos`, computes the local offset within the containing `SourceFile`.
context_after:         let idx = self.lookup_source_file_idx(bpos);