function send(event) {
  var _transition = transition(reach_tooltip_esm_state, event),
      value = _transition.value,
      context = _transition.context,
      changed = _transition.changed;

  if (changed) {
    reach_tooltip_esm_state = {
      value: value,
      context: context
    };
    notify();
  }
}
Send an event to our state machine to find the next state from the current
state + action.

It also manages lifecycles of the machine, (enter/leave hooks on the state
chart)

@param event
@param payload