syntax_data: {"ast_node_type":"other","tokens":[{"end":44,"kind":"keyword","start":0,"text":"(modifier.unwrap_or('x'),"}]}
source_snippet:             (modifier.unwrap_or('x'), index)
context_before:         let (prefix, index) = if let Some(index) = self.reg_index() {
context_after:         } else if let Some(index) = self.vreg_index() {