lanx@nc10-ubuntu:~$ perl
use re 'debug';
my $a=qr/(?<C>1)(?<D>2)(3)(?<A>4)/;
Compiling REx "(?<C>1)(?<D>2)(3)(?<A>4)"
Final program:
   1: OPEN1 'C' (3)
   3:   EXACT <1> (5)
   5: CLOSE1 'C' (7)
   7: OPEN2 'D' (9)
   9:   EXACT <2> (11)
  11: CLOSE2 'D' (13)
  13: OPEN3 (15)
  15:   EXACT <3> (17)
  17: CLOSE3 (19)
  19: OPEN4 'A' (21)
  21:   EXACT <4> (23)
  23: CLOSE4 'A' (25)
  25: END (0)
anchored "1234" at 0 (checking anchored) minlen 4 
Freeing REx: "(?<C>1)(?<D>2)(3)(?<A>4)"