title: Understanding KVO in iOS
body: <p>Regarding "Ensuring KVO Compliance",
  there are some official definition which seem like hard to understand </p>
  
  <blockquote>
    <p>In order to be considered
    KVO-compliant for a specific property,
    a class must ensure the following;</p>
    
    <ol>
    <li><p>The class must be key-value coding
    compliant for the property as
    specified in Ensuring KVC Compliance.</p></li>
    <li><p>The class must allow automatic
    observer notifications for the
    property, or implement manual
    key-value observing for the property.</p></li>
    </ol>
  </blockquote>
  
  <p>Who can give more specific examples to make this more clear ?  Thanks </p>