title: Get partial errors from NSError
body: <p>When using CloudKit, sometimes the error returned is <code>PartialFailure</code>, which may caused by duplicate subscriptions, etc. See example below.</p>
  
  <pre><code>&lt;CKError 0x7f8318711520: "Partial Failure" (2/1011); 
  "Failed to modify some subscriptions"; uuid = A434B010-7650-4BBA-8A7A-33CD0690FD15; 
  container ID = "iCloud.xxx.xxx"; partial errors: { 
  EFC65F4A-A595-44A3-A022-323D9CE9B535 = &lt;CKError 0x7f831a007be0: "Server Rejected Request" (15/2032); server message = "subscription is duplicate of '_930081460_AA87A676-DE57-4530-8BB8-7465BF4F4303'"&gt; 
  C4913907-28F3-42DB-8455-9966D9084834 = &lt;CKError 0x7f83185cfc20: "Server Rejected Request" (15/2032); server message = "subscription is duplicate of '_930081460_F92FA91D-3E92-4E46-AE59-E912F8871026'"&gt; }&gt;
  </code></pre>
  
  <p>I wish to retrieve these partial errors from the main error object but I don't know how. <code>NSError</code> doesn't have a <code>partialError</code> property, and it neither has <a href="https://developer.apple.com/library/mac/documentation/Cocoa/Reference/Foundation/Classes/NSError_Class/Reference/Reference.html#//apple_ref/doc/uid/20001704-CJBIAHGF" rel="nofollow">a key</a> in <code>userInfo</code> to retrieve that.</p>