updated to correct language testing a few (simple - no refactoring or additional conditions, etc) additions to your code:
#!/usr/bin/perl 
my $a = "123{12\n";
print "ACK digit! per cazz posix\n" if ($a =~ /[:^digit:]/);
print "\npast cazz posix\n";

print "ACK digit! per ww-digit-posix\n" if ($a =~ /[^:digit:]/);
print "\tpast ww posix\n";

print "ACK digit! per ww-ISdigit-posix\n" if ($a =~ /[^:isdigit:]/);
print "\tpast ww ISdigit-posix\n";

print "ACK ISdigit! per cazz-ISdigit-posix\n" if ($a =~ /[:^isdigit:]/
+);
print "\npast cazz ISdigit posix\n";

print "ACK \\D!\n" if ($a =~ /\D/);

[download]
Output from CL execution of perl cazz.pl

past cazz posix
ACK digit! per ww-digit-posix
past ww posix
ACK digit! per ww-ISdigit-posix
past ww ISdigit-posix

past cazz ISdigit posix
ACK \D!

But: 
print "ACK digit! per ww-ISdigit-posix\n" if ($a =~ /[[^:isdigit:]]/);
+  #changed; dbl brkts

[download]
changes output:
past cazz posix
ACK digit! per ww-digit-posix
past ww posix
past ww ISdigit-posix <!----

past cazz ISdigit posix
ACK \D!

In reply to Re: negating POSIX regexp classes doesn't work as expected by ww
in thread negating POSIX regexp classes doesn't work as expected by cazz

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