code: protected function hasInLookup(/*# string */ $key)/*# : bool */
      {
          foreach ($this->lookup_pool as $registry) {
              if ($this->hasInRegistry($registry, $key)) {
                  $this->cache_key = $key;
                  $this->cache_reg = $registry;
                  return true;
              }
          }
          return false;
      }
docs: check existence in the whole lookup pool
  
  @param  string $key
  @return bool
  @access protected