title: Regular expression to detect Internet Explorer 11
body: <p>I am using this <code>preg_match</code> string </p>
  
  <pre><code>preg_match('/Trident/7.0; rv:11.0/',$_SERVER["HTTP_USER_AGENT"]
  </code></pre>
  
  <p>to detect IE11 so I can enable tablet mode for it. However it returns "unknown delimiter 7".</p>
  
  <p>How can I do this without PHP complaining at me?</p>