code: public static function base($protocol = null): string {
          if ($protocol === null) {
              return \Mii::$app->base_url;
          }
  
          if ($protocol === TRUE) {
              return \Mii::$app->request->get_hostname() . \Mii::$app->base_url;
          }
  
          if ($protocol !== '//')
              $protocol = $protocol . '://';
  
          $domain = isset($_SERVER['HTTP_HOST']) ? $_SERVER['HTTP_HOST'] : $_SERVER['SERVER_NAME'];
  
  
          return $protocol . $domain . \Mii::$app->base_url;
      }
docs: Gets the base URL to the application.
  To specify a protocol, provide the protocol as a string or request object.
  If a protocol is used, a complete URL will be generated using the
  `$_SERVER['HTTP_HOST']` variable.
  
  // Absolute URL path with no host or protocol
  echo URL::base();
  
  // Absolute URL path with host, https protocol
  echo URL::base('https');
  
  // Absolute URL path with '//'
  echo URL::base('//');
  
  @param   mixed $protocol Protocol string or boolean
  @return  string