function participantRoleString()
 {
     if ($this->ParticipantRole < self::ROLE_CUSTOM) {
         return eZCollaborationItemParticipantLink::roleString($this->ParticipantRole);
     }
     $item = eZCollaborationItem::fetch($this->CollaborationID);
     return $item->attribute('type_identifier') . '_' . $item->handler()->participantRoleString($this->ParticipantRole);
 }