{"ast_node_type":"other","tokens":[{"end":55,"kind":"keyword","start":0,"text":"///"}]}
    /// with the name of the crate containing the impl.
    /// Looks up the span of `impl_did` if the impl is local; otherwise returns `Err`
    pub fn span_of_impl(self, impl_def_id: DefId) -> Result<Span, Symbol> {