use Devel::Peek qw( Dump );
$_ = "x" x 999;
$_ .= "x";  # Force unsharing.
Dump( $_ );
$_ = "abc";
Dump( $_ );

##</code><code>##

SV = PV(0x5b5d1f3fdee0) at 0x5b5d1f439bc8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x5b5d1f441580 "xxx[...]xxx"\0
  CUR = 1000
  LEN = 1001
SV = PV(0x5b5d1f3fdee0) at 0x5b5d1f439bc8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x5b5d1f441580 "abc"\0    <-- Same buffer
  CUR = 3
  LEN = 1001                     <-- Same size

##</code><code>##

use Devel::Peek qw( Dump );
$_ = "abcdefghi";
$_ .= "j";  # Force unsharing.
Dump( $_ );
substr( $_ , 0 , 1 ) = "";
Dump( $_ );

##</code><code>##

SV = PV(0x600760853ee0) at 0x6007608a35d8
  REFCNT = 1
  FLAGS = (POK,pPOK)
  PV = 0x60076086a2e0 "abcdefghij"\0
  CUR = 10
  LEN = 16
SV = PV(0x600760853ee0) at 0x6007608a35d8
  REFCNT = 1
  FLAGS = (POK,OOK,pPOK)
  OFFSET = 1
  PV = 0x60076086a2e1 ( "\x01" . ) "bcdefghij"\0
  CUR = 9
  LEN = 15