title: iPhone: How to detect if an EKEvent instance can be modified?
body: <p>While working with the EventKit on iPhone I noticed that some events can exist which cannot be modified. Examples I encountered so far are birthdays and events synced with CalDAV. When you view the event's details in the standard built-in calendar app on iPhone the "Edit" button in the top-right corner is not visible in these cases, where it would be visible when viewing "normal" events.</p>
  
  <p>I've searched everywhere, read all documentation there is but I simply can't find anything that tells me how to detect this behavior! I can only detect it afterwards:</p>
  
  <ol>
  <li>edit an event's title</li>
  <li>save it to the event store</li>
  <li>check the event's title, if it has not changed it is not editable!</li>
  </ol>
  
  <p>I am looking for a way that I can detect the non-editable behavior of an event beforehand. I know this is possible because I've seen other calendar apps implement this correctly.</p>