public function __construct($attributes = array(), Item $relatedItem = null, $serial = '')
 {
     parent::__construct($attributes, $relatedItem, $serial);
     if (class_exists(static::$containerType)) {
         $this->body = new static::$containerType('', $relatedItem);
     } else {
         throw new QtiModelException('The container class does not exist: ' . static::$containerType);
     }
 }
 public function __construct($attributes = array(), Item $relatedItem = null, $serial = '')
 {
     parent::__construct($attributes, $relatedItem, $serial);
     //init the two matchSets: a double array
     $this->choices = array(array(), array());
 }
 public function __construct($attributes = array(), Item $relatedItem = null, $serial = '')
 {
     parent::__construct($attributes, $relatedItem, $serial);
     $this->object = new Object();
 }