title: Unknown modifier '(' when using preg_match() with a REGEX expression
body: <p>I'm trying to validate dates like DD/MM/YYYY with PHP using preg_match(). This is what my REGEX expression looks like:</p>
  
  <pre><code>$pattern = "/^([123]0|[012][1-9]|31)/(0[1-9]|1[012])/(19[0-9]{2}|2[0-9]{3})$/";
  </code></pre>
  
  <p>But using it with a correct value, I get this message: </p>
  
  <blockquote>
    <p>preg_match(): Unknown modifier '('</p>
  </blockquote>
  
  <p>Complete code:</p>
  
  <pre><code>    $pattern = "/^([123]0|[012][1-9]|31)/(0[1-9]|1[012])/(19[0-9]{2}|2[0-9]{3})$/";
      $date = "01/03/2011";
  
      if(preg_match($pattern, $date)) return TRUE;
  </code></pre>
  
  <p>Thank you in advance</p>