code: protected function resolveReference(/*# string */ $name)
      {
          // lookup the reference
          $val = $this->referenceLookup($name);
  
          // dealing with unknown reference
          if (is_null($val)) {
              $val = $this->resolveUnknown($name);
          }
          return $val;
      }
docs: Resolve the reference $name
  
  @param  string $name
  @return mixed
  @throws RuntimeException if reference unknown
  @access protected
  @since  2.0.8 added localCache support
  @since  2.0.13 removed localCache support