code: protected function addRegistry($registry)
      {
          // remove it if exists already
          $this->removeFromLookup($registry);
  
          // set delegator in registry
          if ($registry instanceof DelegatorAwareInterface) {
              $registry->setDelegator($this);
          }
  
          // append to the pool
          $this->lookup_pool[] = $registry;
  
          return $this;
      }
docs: Append one registry to lookup pool
  
  @param  object $registry
  @return $this
  @access protected