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<?php var_dump(preg_match('/((?1)?z)/', '')); var_dump(preg_last_error() === \PREG_NO_ERROR);
Finding entry points
Branch analysis from position: 0
1 jumps found. (Code = 62) Position 1 = -2
filename:       /in/UkeMa
function name:  (null)
number of ops:  14
compiled vars:  none
line      #* E I O op                           fetch          ext  return  operands
-------------------------------------------------------------------------------------
    3     0  E >   INIT_FCALL                                               'var_dump'
          1        INIT_FCALL                                               'preg_match'
          2        SEND_VAL                                                 '%2F%28%28%3F1%29%3Fz%29%2F'
          3        SEND_VAL                                                 ''
          4        DO_ICALL                                         $0      
          5        SEND_VAR                                                 $0
          6        DO_ICALL                                                 
    4     7        INIT_FCALL                                               'var_dump'
          8        INIT_FCALL                                               'preg_last_error'
          9        DO_ICALL                                         $2      
         10        IS_IDENTICAL                                     ~3      $2, 0
         11        SEND_VAL                                                 ~3
         12        DO_ICALL                                                 
         13      > RETURN                                                   1

Generated using Vulcan Logic Dumper, using php 8.0.0


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