syntax_data: {"ast_node_type":"other","tokens":[{"end":44,"kind":"keyword","start":0,"text":"start_pos:"}]}
source_snippet:             start_pos: BytePos::from_u32(0),
context_before:             external_src: FreezeLock::frozen(ExternalSource::Unneeded),
context_after:             source_len: RelativeBytePos::from_u32(source_len),