function _beginpage($orientation, $size)
 {
     parent::_beginpage($orientation, $size);
     if ($this->NewPageGroup) {
         // start a new group
         $n = sizeof($this->PageGroups) + 1;
         $alias = '{' . $n . '}';
         $this->PageGroups[$alias] = 1;
         $this->CurrPageGroup = $alias;
         $this->NewPageGroup = false;
     } elseif ($this->CurrPageGroup) {
         $this->PageGroups[$this->CurrPageGroup]++;
     }
 }