What's with people not checking for errors and warnings when their code doesn't work?

Use of uninitialized value $+{"intern"} in regexp compilation at a.pl 
+line 6.
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It actually fails when any recursion is needed. The initial expression doesn't actually exercise the recursive path, which is why it works.

The problem results in $cparens containing

(?x-ism:
(?<intern>
 \<
 (?:
  [^<>]++
  |
  (?)
 )*+
 \>
)
)
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Replace

(?$+{intern})
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with

(?&intern)
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