So setting an attribute sounds okay if we don't like passing this state in the url. If you look at https://github.com/mozilla-b2g/gaia/blob/master/apps/calendar/js/views/event_base.js#L268, the way this._returnTop gets set on the view before the patch is that this.returnTo_ gets set to router.last and then this.returnTop_ gets set to this.returnTo_. We have a bit of an unusual case here because we want returnTo to be the event show view and we want returnTop to be one of day, week, or month.