public function set($name, $value)
 {
     if ($name == 'qs') {
         if ($value !== null) {
             $this->_qs = new Query_String($value);
         } else {
             $this->_qs = null;
         }
     } else {
         parent::set($name, $value);
     }
 }
 public function set($name, $value)
 {
     parent::set($name, $value);
     if ($this->_datetime !== null) {
         if ($value === null) {
             throw new Invalid_Argument_Value_Exception($name, $value);
         }
         if ($name == 'timestamp') {
             $this->updateByTimestamp();
         } else {
             $this->updateTimestamp();
         }
     }
 }