DNS lookup
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... S-NAPTR, the REPLACEMENT field is
used as the target of the next DNS lookup -- for NAPTR RRs.
...
...
o the S-NAPTR-designated DNS lookup fails to yield expected results
-- e.g., no A RR for an "A" target ...
...
o entwine the application-specific protocol with the DNS lookup and
RRset processing described in the pseudocode ...