[DNSOP] how to delete obsolete DS for obsolete DNSKEY using CDS/CDNSKEY

[神明達哉 <[e-mail]>]

I have one quick question about CDS/CDNSKEY: what's the (or "an")
expected operation for the parent to remove a DS RR of a child that
was obsolete and is now removed from the child zone?

This point is not clear to me on a quick rescan of
draft-ietf-dnsop-delegation-trust-maintainance-02.

According to Section 3:

   The CDS / CDNSKEY record is published in the child zone and gives the
   child control of what is published for it in the parental zone.  The
   CDS / CDNSKEY RRset expresses what the child would like the DS RRset
   to look like after the change; [...]

it could read the child would remove the CDS or CDSKEY for the
now-removed DNSKEY, but it may contradict Section 4.1:

   Absence of CDS / CDNSKEY in child signals "No change" to the current
   DS set.

(BTW: this sentence is a bit ambiguous to me.  Does this mean there's
no CDS/CDNSKEY RR for the apex name, or the absence of CDS/CDNSKEY for
a specific DNSKEY?)

and also Section 5:

   When the Parent DS is "in-sync" with the CDS, the Child DNS Operator
   MAY delete the CDS RRset.

i.e., if the child may delete a CDS for a new DNSKEY after
synchronization, clearly it cannot use the removal of CDS as an
indication of the removal of DNSKEY.

Am I missing some part of the draft that answers my question, or is
this actually out of scope of CDS/CDNSKEY?

p.s. apologize in advance this was already discussed; I don't remember
all previous discussions of the proposal.

--
JINMEI, Tatuya