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  1. <?php 
  2.  
  3.  
  4.  
  5. $s = '
  6. AAA
  7. //content
  8. :AAA
  9. ';
  10. // this pattern does not match, because of the named subpattern in the first alternative of the condition on recursion?
  11. $p1 = '~(?J)
  12.  
  13. (?(R)
  14.     (?P<tag>ZZZ)        # with the given subject, recursion shall never occur and thus never use this alternative
  15. |
  16.     (?P<tag>AAA)        # with the given subject, recursion shall never occur and thus always use this alternative
  17. )
  18.  
  19. [^:]+                   # matching //content
  20.  
  21. :(?P=tag)               # matching :AAA (last line)
  22.  
  23. ~mx';
  24.  
  25.  
  26. // this pattern matches
  27. $p2 = '~(?J)
  28.  
  29. (?(R)
  30.     ZZZ                 # the only difference with pattern $p1 is this line (no tag used)
  31. |
  32.     (?P<tag>AAA)
  33. )
  34.  
  35. [^:]+
  36.  
  37. :(?P=tag)
  38.  
  39. ~mx';
  40.  
  41. // this pattern matches
  42. $p3 = '~(?J)
  43.  
  44. (?(R)
  45.     (?P<tag>ZZZ)
  46. |
  47.     (?P<tag>AAA)
  48. )
  49.  
  50. [^:]+
  51.  
  52. :\2                     # the only difference with pattern $p1 is this line (no tag used)
  53.  
  54. ~mx';
  55.  
  56.  
  57. $p = $p1;
  58. //$p=$p2;    // It seems that the named tag in the first alternative causes problem
  59. //$p=$p3;    // It seems that the second alternative was captured indeed, but cannot be backreferenced with its name
  60.  
  61. if (preg_match($p, $s, $m)) {
  62.     echo 'ok';
  63. }
  64. else{
  65.     echo 'oops';
  66. }
Success #stdin #stdout 0.01s 20520KB
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Standard input is empty
stdout
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oops
https://ideone.com/NuORid
language:
PHP (php 7.3.5)
created:
10 years ago
visibility:
secret

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