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

In reply to Re^3: Escaping special characters by james28909
in thread Escaping special characters by tiny_monk

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.