title: Crazy Confusing PHP OOP "implements" "extends" at the same time
body: <pre><code>abstract class SF_Model_Acl_Abstract 
      extends SF_Model_Abstract
      implements SF_Model_Acl_Interface, Zend_Acl_Resource_Interface
  {
      protected $_acl;
      protected $_identity;
      public function setIdentity($identity)
      {
      if (is_array($identity)) {
          ......
          ......
  </code></pre>
  
  <p>Can you help me explain how it can "<code>implements</code>" "<code>extends</code>" at the same time?
  <br>Does it just combine the 3 class together? </p>
  
  <p>I am totally confused!</p>