code: function() {
  		// counting that dates were sorted in initialization
  		var date = this.events[0].start_date;
  		if (this.eras && this.eras.length > 0) {
  			if (this.eras[0].start_date.isBefore(date)) {
  				return this.eras[0].start_date;
  			}
  		}
  		return date;
  
  	}
docs: Return the earliest date that this config knows about, whether it's a slide or an era