/**
  * set the desceneder value
  * @param numeric $descender
  **/
 public function setDescender($descender)
 {
     if ($this->direction == -1) {
         foreach ($this->directions as $direction) {
             $this->font_metrics[$direction]->setDescender($descender);
         }
         parent::setDescender($descender);
     } else {
         $this->font_metrics[$this->direction]->setDescender($descender);
     }
 }