{"ast_node_type":"other","tokens":[{"end":83,"kind":"keyword","start":0,"text":"///"}]}
    ///   or they may not be adjacent, due to arbitrary numbers of 1ZST fields that
    /// - `a` and `b` will have a different FieldIdx, but otherwise `b`'s may be lower
    ///   will not affect the shape of the data which determines if `Pair` will be used.