code: function() {
          var C = YAHOO.widget.CalendarNavigator.CLASSES;
  
          var d = this._doc.createElement("div");
          d.className = C.MASK;
  
          this.cal.oDomContainer.appendChild(d);
          this.maskEl = d;
      }
docs: Creates the Mask HTMLElement and appends it to the Calendar/CalendarGroups
  container.
  
  @method createMask