code: public function render($mainName = 'default', $barName = false, array $data = null)
      {
          // set the default value if nothing was passed
          if ($data === null) {
              $data = ['title' => 'Navigation', 'side' => 'dropdown', 'inverse' => true];
          }
  
          // get the nav bar arrays
          $main = $this->getMain($mainName);
          if (is_string($barName)) {
              $bar = $this->getBar($barName);
              if (empty($bar)) {
                  $bar = false;
              }
          } else {
              $bar = false;
          }
  
          // return the html nav bar
          return $this->view->make($this->name, array_merge($data, ['main' => $main, 'bar' => $bar]))->render();
      }
docs: Get the navigation bar html.
  
  @param string      $mainName
  @param string|bool $barName
  @param array|null  $data
  
  @return string