A Naming Authority Pointer record (RFC 3403).
Flags controlling the rewrite (e.g. S, A, U, P).
S
A
U
P
Processing order (lower first).
Tie-break preference among equal orders.
The substitution regular expression.
The replacement domain name.
The service field (e.g. SIP+D2U).
SIP+D2U
A Naming Authority Pointer record (RFC 3403).