code: function() {
      this._unsetFirstRow();
      var elTr = this.getFirstTrEl();
      if(elTr) {
          // Set FIRST
          Dom.addClass(elTr, DT.CLASS_FIRST);
          this._sFirstTrId = elTr.id;
      }
  }
docs: Assigns the class YAHOO.widget.DataTable.CLASS_FIRST to the first TR element
  of the DataTable page and updates internal tracker.
  
  @method _setFirstRow
  @private