use Data::Dumper;
my $re_bad  = qr'xx([A-Z$#@_!]*) (?! [A-Za-z0-9$#@_] )'x;
print $re_bad;

##</code><code>##

(?x-ism:xx([A-Z$#@_!]*) (?! [A-Za-z0-9$#@_] )#
)

##</code><code>##

my $re_bad  = qr'xx([A-Z$#@_!]*) (?! [A-Za-z0-9$#@_] )'x;
print $re_bad;

##</code><code>##

(?x-ism:xx([A-Z$#@_!]*) (?! [A-Za-z0-9$#@_] ) 
)