title: PHP's filter_var() Function Generating Warning
body: <p>Does any body know why the filter_var() function below is generating the warning? Is there a limit on how many characters can be in a character class?</p>
  
  <pre><code>$regex = "/^[\w\041\042\043\044\045\046\047\050\051\052\053\054\055\056\057\072\073\074\075\076\077\100\133\134\135\136\140\173\174\175\176]*$/";
  
  $string = "abc";
  
  if(!filter_var($string, FILTER_VALIDATE_REGEXP, array("options" =&gt; array("regexp"=&gt;$regex))))
  {
      echo "dirty";
  }
  
  else
  {
      echo "clean";
  }
  </code></pre>
  
  <p>Warning: filter_var() [function.filter-var]: Unknown modifier ':'</p>