title: basic bootstrap implementation results in blank page
body: <p>I've tried implementing the basics for bootstrap into an xmb forum templare but all I get is a blank page. </p>
  
  <p>Prior to bootstrap:</p>
  
  <pre><code>&lt;?xml version=\"1.0\" encoding=\"$charset\"?&gt;
  &lt;!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\"&gt;
  &lt;html xmlns=\"http://www.w3.org/1999/xhtml\"&gt;
  
  &lt;!-- $versionlong  --&gt;
  &lt;!-- Build: $versionbuild --&gt;
  &lt;!-- $versioncompany --&gt;
  &lt;head&gt;
  
  $baseelement$canonical_link
  
  &lt;title&gt;{$SETTINGS[\'bbname\']} $threadSubject - $versionlong&lt;/title&gt;
  
  $css
  
  &lt;script language=\"JavaScript\" type=\"text/javascript\" src=\"./js/header.js\"&gt;&lt;/script&gt;
  
  &lt;/head&gt;
  </code></pre>
  
  <p>and after bootstrap code:</p>
  
  <pre><code>&lt;!-- ?xml version=\"1.0\" encoding=\"$charset\"? --&gt;
  &lt;!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Transitional//EN\" \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd\"&gt;
  &lt;html xmlns=\"http://www.w3.org/1999/xhtml\"&gt;
  
  &lt;!-- $versionlong  --&gt;
  &lt;!-- Build: $versionbuild --&gt;
  &lt;!-- $versioncompany --&gt;
  &lt;head&gt;
  
  &lt;!-- Required meta tags --&gt;
      &lt;meta charset=\"$charset\"&gt;
      &lt;meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no"&gt;
  
  $baseelement$canonical_link
  
  &lt;title&gt;{$SETTINGS[\'bbname\']} $threadSubject - $versionlong&lt;/title&gt;
  
  &lt;!-- $css --&gt;
  
  &lt;script language=\"JavaScript\" type=\"text/javascript\" src=\"./js/header.js\"&gt;&lt;/script&gt;
  
  &lt;!-- Bootstrap CSS --&gt;
      &lt;link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0-beta/css/bootstrap.min.css" integrity="sha384-/Y6pD6FV/Vv2HJnA6t+vslU6fwYXjCFtcEpHbNJ0lyAFsXTsjBbfaDjzALeQsN6M" crossorigin="anonymous"&gt;
  
  
  &lt;/head&gt;
  </code></pre>
  
  <p>Any clues as to the issue[s] appreciated.</p>