placeHolder (placeHolder) {
        if (!arguments.length) {
            return this._placeHolder;
        }
        this._placeHolder = placeHolder;
        return this;
    }
Placeholder text in the search box.
@example
// This is the default
chart.placeHolder('type to filter');
@param {function} [placeHolder='search']
@returns {TextFilterWidget|string}