Metadata and DNSSEC

SAML 2.0 Metadata states:

  4.3.3.1 Processing Signed DNS Zones

  Verification of DNS zone signature SHOULD be processed, if present, as
described in [RFC2535].

RFC2535 was obseleted by RFCs 4033-5 (one month after the publication of
SAMLMeta2). Can anyone clarify what, if any, consideration has been
given to this?

Thanks, josh.