Indeed! I misunderstood the documentation.

use 5.010;  # re features
use strict;
use warnings;

for ('abcdef') {
   m{
      (?(DEFINE)
         (?<x>
            (?<i1> . ) (?<i2> . )
            (?{ '...' })
         )
         (?<y>
            (?<i1> . ) (?<i2> . )
            (?{ print("($+{i1},$+{i2})") })
         )
         (?<z>
            (?<i1> . ) (?<i2> . )
            (?{ '...' })
         )
      )

      (?&y)+
   }x;
}

print("\n");
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