I personally do not see an exclamation point in Metacharacters but if your just trying to remove the '!' from user input, whether it be Perl or HTML, please take this into consideration:

use strict;
use warnings;

while (<DATA>){
print "Perl string - ", my $perl_string = $_ =~ s/!//rg if $_ !~ /<.*?
+>/g;
print "HTML string - ", my $html_string = $_ =~ s/!//rg if $_ =~ /<.*?
+>/g;
}

__DATA__
123!!!!!!
<p>123!!!!!</p>
[download]

As for the security of your website, I think I will leave that to some professionals ;) Update: Changed link, thanks soonix