The steps taken to 'uniqify' the characters of the character set are not necessary; repeated characters in a regex character set have no effect on pattern recognition. (I also think repeated characters make no difference in the execution time of the regex, but I cannot come up with a reference on this at the moment.) However, repeated characters do seem to take up space in the regex object. 
>perl -wMstrict -le
"my $standard = 'ABCAAAABBBCCCCCAAABBBCCC';
 foreach (@ARGV) {
   my $non_standard = /[^$standard]/;
   print qq{'$_' }, $non_standard ? 'no match' : 'match';
   }
"
"" A B C ABC ABCABCABC xA Ax xABC ABCx
'' match
'A' match
'B' match
'C' match
'ABC' match
'ABCABCABC' match
'xA' no match
'Ax' no match
'xABC' no match
'ABCx' no match

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In reply to Re^2: Match only certain characters? by AnomalousMonk
in thread Match only certain characters? by Anonymous Monk

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