title: Symfony Routing Regex: How to write an optional character?
body: <p>I just have a little trouble with the symfony regex pattern in a routing config.</p>
  
  <p>I would like to match both <code>/keyword</code> and <code>/keyword/</code> URLs. The <code>/</code> character is optional.<br>
  Here is my pattern :</p>
  
  <pre><code>pattern:  /{keyword}/?
  </code></pre>
  
  <p><code>/keyword/</code> matches the pattern, while <code>/keyword</code> does not.</p>
  
  <p>How should I write the pattern ?</p>