sv_usepvn_flags(x, dx, 8, SV_HAS_TRAILING_NUL);

##</code><code>##

sv_usepvn_flags(x, dx, 7, SV_HAS_TRAILING_NUL);

##</code><code>##

sv_usepvn_flags(x, dx, strlen(dx), SV_HAS_TRAILING_NUL);

##</code><code>##

SvREADONLY_on(x);

##</code><code>##

SV = PV(0x3e1a1785e0) at 0x3e1a197528
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x35260c8bbd5 "dddddd"       <-- Pointer into C static storage
  CUR = 6
  LEN = 0                           <-- Doesn't belong to Perl.

##</code><code>##

SV = PV(0x3e1a1785e0) at 0x3e1a197528
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x3e1a19fe50 "dddddda"\0     <-- New buffer (copy + "a")
  CUR = 7
  LEN = 17                          <-- Belongs to Perl.