code: func FlashFilter(c *Controller, fc []Filter) {
  	c.Flash = restoreFlash(c.Request)
  	c.ViewArgs["flash"] = c.Flash.Data
  
  	fc[0](c, fc[1:])
  
  	// Store the flash.
  	var flashValue string
  	for key, value := range c.Flash.Out {
  		flashValue += "\x00" + key + ":" + value + "\x00"
  	}
  	c.SetCookie(&http.Cookie{
  		Name:     CookiePrefix + "_FLASH",
  		Value:    url.QueryEscape(flashValue),
  		HttpOnly: true,
  		Secure:   CookieSecure,
  		Path:     "/",
  	})
  }
docs: // FlashFilter is a Revel Filter that retrieves and sets the flash cookie.
  // Within Revel, it is available as a Flash attribute on Controller instances.
  // The name of the Flash cookie is set as CookiePrefix + "_FLASH".