docs: function(valstr , a , b , d , p){
      this.setDate("_a" , a || null);
      this.setDate("_b" , b || null);
     
      this._d = d || null; // duration
      this._p = p || null; // period
  
      if (valstr){
          this.__string__ = valstr;
          this.parse(valstr)
      }
  }