code: public function prependPath($path, $namespace = self::MAIN_NAMESPACE)
      {
          // invalidate the cache
          $this->cache = $this->errorCache = array();
  
          $checkPath = $this->isAbsolutePath($path) ? $path : $this->rootPath.$path;
          if (!is_dir($checkPath)) {
              throw new Twig_Error_Loader(sprintf('The "%s" directory does not exist ("%s").', $path, $checkPath));
          }
  
          $path = rtrim($path, '/\\');
  
          if (!isset($this->paths[$namespace])) {
              $this->paths[$namespace][] = $path;
          } else {
              array_unshift($this->paths[$namespace], $path);
          }
      }
docs: Prepends a path where templates are stored.
  
  @param string $path      A path where to look for templates
  @param string $namespace A path namespace
  
  @throws Twig_Error_Loader