code: public function buildReferenceLookupTable($strNodeName, $strIndexAttribute = 'name')
      {
  
          $arrOut = array();
  
          if (!isset($this->$strNodeName)) {
              return array();
          }
  
          foreach ($this->$strNodeName as $objNode) {
              $strIndex = (string)$objNode->attributes()->$strIndexAttribute;
              $arrOut[$strIndex] = $objNode;
          }
  
          return $arrOut;
      }
docs: Build an array with references to subnodes of this xml element
  Indexed by an urified index attribute (standard 'name')
  
  @param string $strNodeName name of the subnode
  @param string $strIndexAttribute name of the attribute used as array index
  @return static[]