title: How to determine whether contacts in iOS are duplicates or not?
body: <p>What criteria does Apple use to determine whether a vCard sent for example as an email attachment has a duplicate? I would think there has to be more in common between the duplicates than just the given name and the family name? Does Apple say whether the given name, family name, and address enough similarities to consider two contacts duplicates of each other?</p>
  <p>I found code in answers on stack<strong>overflow</strong>, but they appear to use the programmers' own criteria instead of Apple's criteria.</p>