syntax_data: {"ast_node_type":"function","tokens":[{"end":53,"kind":"keyword","start":0,"text":"pub"}]}
source_snippet:     pub fn guess_head_span(&self, sp: Span) -> Span {
context_before:     /// *Only suitable for diagnostics.*
context_after:         // FIXME: extend the AST items to have a head span, or replace callers with pointing at