syntax_data: {"ast_node_type":"other","tokens":[{"end":51,"kind":"keyword","start":0,"text":"//"}]}
source_snippet:     // advance to contain the multi-byte character.
context_before:     // An empty span pointing just before a multi-byte character should
context_after:     let span = Span::with_root_ctxt(BytePos(1), BytePos(1));