syntax_data: {"ast_node_type":"other","tokens":[{"end":53,"kind":"keyword","start":0,"text":"span_interner:"}]}
source_snippet:     span_interner: Lock<span_encoding::SpanInterner>,
context_before:     symbol_interner: symbol::Interner,
context_after:     /// Maps a macro argument token into use of the corresponding metavariable in the macro body.