title: What is an undocumented method and a private API?
body: <p>Recently I have get a reject from Apple because a use of a private API. I don't know exactly what is a private API nor an undocumented method. Could someone explain me what is an undocumented method and a private API? I'm really confused with that...</p>
  
  <p><strong>Follow up:</strong></p>
  
  <ul>
  <li>What is exactly the "official documentation"? Can I use some frameworks and classes made by thirds such as the Amazon one?</li>
  </ul>