t states are not visible or editable by the user, but
  the back and forward buttons can still be used to move between history states.
  </p>

  <p>Try setting a few history tokens using the buttons and box below, then hit
  the back and forward buttons to test if the tokens are correctly restored.</p>

  <button onclick="setToken('one')">State 1</button>
  <button onclick="setToken('two')">State 2</button>
  <button onclick="setToken('three')">State 3</button>
  <button onclick="setToken('four')">State 4</