docs: function(rrule) {
      this.rrule = rrule;
      this.lastyear = null;
      this.lastmonth = null;
      this.yearlen = null;
      this.nextyearlen = null;
      this.yearordinal = null;
      this.yearweekday = null;
      this.mmask = null;
      this.mrange = null;
      this.mdaymask = null;
      this.nmdaymask = null;
      this.wdaymask = null;
      this.wnomask = null;
      this.nwdaymask = null;
      this.eastermask = null;
  }