code: public function setLayout($layout)
      {
          if ($layout === "" || $layout === null) {
              $this->layout = null;
          } else {
              $layoutPath = $this->templatePath . $layout;
              if (!is_file($layoutPath)) {
                  throw new \RuntimeException("Layout template `$layout` does not exist");
              }
              $this->layout = $layoutPath;
          }
      }
docs: Set layout template
  
  @param string $layout