For a menu to be accessible it needs to work for:

  • Mouse users
  • Touch screen users
  • Keyboard-only users
  • Screen reader users

Full-toggle disclosure nav example (Bootstrap):

Split-toggle disclosure nav example:

Other accessible options exist, like a split toggle. It uses a similar technique but allows for the top-level link (Messages) to be clickable and go to a webpage.  The down arrow would become a toggle button.

menu item with a split toggle