filterPrinter (filterPrinterFunction) {
        if (!arguments.length) {
            return this._filterPrinter;
        }
        this._filterPrinter = filterPrinterFunction;
        return this;
    }
Set or get the filter printer function. The filter printer function is used to generate human
friendly text for filter value(s) associated with the chart instance. The text will get shown
in the `.filter element; see {@link BaseMixin#turnOnControls turnOnControls}.

By default dc charts use a default filter printer {@link printers.filters printers.filters}
that provides simple printing support for both single value and ranged filters.
@example
// for a chart with an ordinal brush, print the filters in upper case
chart.filterPrinter(function(filters) {
  return filters.map(function(f) { return f.toUpperCase(); }).join(', ');
});
// for a chart with a range brush, print the filter as start and extent
chart.filterPrinter(function(filters) {
  return 'start ' + utils.printSingleValue(filters[0][0]) +
    ' extent ' + utils.printSingleValue(filters[0][1] - filters[0][0]);
});
@param {Function} [filterPrinterFunction=printers.filters]
@returns {Function|BaseMixin}