Add some information about array overloading

Zend/ZEND_CHANGES

@@ -890,6 +890,47 @@ Changes in the Zend Engine 2.0
       the use of all abstract methods declared in the interfaces Iterator
       and IteratorAggregate respectively.
 
+    * Array overloading
+
+      Objects can be used with Array notation when they implement the 
+      interface ArrayAccess. You cannot use such objects in standard
+      array functions, however you have full control over the array
+      notation. This allows lazy initialization or read only array.
+
+      Note that setting [] results in a call to offsetSet() with
+      index being NULL. That means that as with standard arrays you 
+      cannot store NULL keys.
+
+      Example:
+
+        <?php
+	        class ArrayClass implements ArrayAccess {
+				public $a = array();
+
+				function offsetExists($index) {
+					return array_key_exists($index, $this->a);
+				}
+				function offsetGet($index) {
+					return $this->a[$index];
+				}
+				function offsetSet($index, $newval) {
+					return $this->a[$index] = $newval;
+				}
+				function offsetUnset($index) {
+					unset($this->a[$index]);
+				}
+			}
+
+			$obj = new ArrayClass;
+
+			$obj[0] = 'bla';     // calls offsetSet(0,'bla')
+			$obj[] = 42;         // calls offsetSet(NULL, 42)
+			$x = $obj[0];        // calls offsetGet(0)
+			$b = isset($obj[0]); // calls offsetExists(0)
+			unset($obj[0]);      // calls offsetUnset(0)
+		?>
+
+
     * __METHOD__
 
       The pseudo constant __METHOD__ shows the current class and method