title: Symfony Routing - Optional parameters
body: <p>I'm creating a Symfony project that outputs JSON for consumption by an iPhone App.</p>
  
  <p>I have a route set up:</p>
  
  <pre><code>notification_json:
    url: /notifications.json
    param: { module: notification, action: index, sf_format: json }
  </code></pre>
  
  <p>This currently lists all notifications (one of my models).</p>
  
  <p>What I'd like to do is add some parameters to this, much like the Twitter API has 'since_id' - so if /notifications.json?since_id=3 was requested, only notifications with an ID higher than 3 would be shown.</p>
  
  <p>I can't see me struggling with the action logic, but the routing for this kind of thing has me scratching my head a little!</p>
  
  <p>Any help would be extremely appreciated.</p>