title: iOS EventKit EKCalendar unique (global) identifier
body: <p>Is there a property that can be used to recognize calendars across devices?</p>
  
  <p>According to the Apple docs, the "calendarIdentifier" property cannot be used:</p>
  
  <blockquote>
    <p>A full sync with the calendar will lose this identifier. You should have a plan for dealing with a calendar whose identifier is no longer fetch-able by caching its other properties.</p>
  </blockquote>
  
  <p>I'm looking for something similar to EKEvent.calendarItemExternalIdentifier, which is the same and unique across devices, but for Calendars.</p>