perl -Dr myprog

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  use re qw{ debug };

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Compiling REx `(un-.*)\@(.*)'
size 17 Got 140 bytes for offset annotations.
first at 3
rarest char @ at 0
rarest char - at 2
   1: OPEN1(3)
   3:   EXACT <un->(5)
   5:   STAR(7)
   6:     REG_ANY(0)
   7: CLOSE1(9)
   9: EXACT <@>(11)
  11: OPEN2(13)
  13:   STAR(15)
  14:     REG_ANY(0)
  15: CLOSE2(17)
  17: END(0)
anchored `un-' at 0 floating `@' at 3..2147483647 (checking anchored) minlen 4 
Offsets: [17]
        1[1] 0[0] 2[3] 0[0] 6[1] 5[1] 7[1] 0[0] 8[135549512] 0[0] 10[1] 0[0] 12[1] 11[1] 13[1] 0[0] 14[0] 
Omitting $` $& $' support.

EXECUTING...
[snip]

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Compiling REx `(un-.*)\@(.*)'

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size 17 Got 140 bytes for offset annotations.

##</code><code>##

first at 3
rarest char @ at 0
rarest char - at 2

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   1: OPEN1(3)
[...]
  17: END(0)

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anchored `un-' at 0 floating `@' at 3..2147483647 (checking anchored) minlen 4 

##</code><code>##

  anchored `n-' at 1 floating `@' at 3..2147483647 (checking anchored) stclass `ANYOF[Uu]' minlen 4 

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Offsets: [17]
        1[1] 0[0] 2[3] 0[0] 6[1] 5[1] 7[1] 0[0] 8[135549512] 0[0] 10[1] 0[0] 12[
+1] 11[1] 13[1] 0[0] 14[0] 

##</code><code>##

Omitting $` $& $' support.