The DNS-error-payload type is currently defined as this:

  /// Defines the case payload type for `DNS-error` above:
  @since(version = 0.2.0)
  record DNS-error-payload {
    rcode: option<string>,
    info-code: option<u16>
  }

This has the rcode value be a string. However, DNS rcodes have standardized values that are defined in terms of u16 values.

With the current type being string, implementations appear to be using ad-hoc error messages which don't correspond to any standardized rcode value.