title: Reveal.js: Conditionally show a slide
body: <p>Suppose I have this reveal.js code:</p>
  
  <pre><code>&lt;section&gt;
      &lt;p&gt;A: Introduction&lt;/p&gt;
  &lt;/section&gt;
  &lt;section&gt;
      &lt;p&gt;B: This slide takes 30 minutes to explain.&lt;/p&gt;
  &lt;/section&gt;
  &lt;section class="notShownInShortPresentation"&gt;
      &lt;p&gt;C: This slide takes 2 hours to explain.&lt;/p&gt;
  &lt;/section&gt;
  &lt;section&gt;
      &lt;p&gt;D: Conclusion&lt;/p&gt;
  &lt;/section&gt;
  &lt;section class="notShownInPDFOutput"&gt;
      &lt;p&gt;E: Click here to print this deck to PDF.&lt;/p&gt;
  &lt;/section&gt;
  </code></pre>
  
  <p>Slide C and E should be shown conditionally:</p>
  
  <ul>
  <li><p>Show <code>notShownInShortPresentation</code> if URL ends with <code>?longDuration</code></p></li>
  <li><p>Show <code>notShownInPDFOutput</code> if URL does not ends with <code>?print-pdf</code></p></li>
  </ul>
  
  <p>Is that possible? If I add <code>style="visilibity: hidden;"</code> on a <code>&lt;section&gt;</code>, that slide doesn't disappear, it's just empty.</p>