beginSlice (beginSlice) {
        if (!arguments.length) {
            return this._beginSlice;
        }
        this._beginSlice = beginSlice;
        return this;
    }
Get or set the index of the beginning slice which determines which entries get displayed by the widget.
Useful when implementing pagination.
@param {Number} [beginSlice=0]
@returns {Number|DataGrid}