text: import CLASS from 'c3-master/src/class';
  import { c3_chart_fn } from 'c3-master/src/core';
  
  c3_chart_fn.regions = function (regions) {
      var $$ = this.internal, config = $$.config;
      if (!regions) { return config.regions; }
      config.regions = regions;
      $$.redrawWithoutRescale();
      return config.regions;
  };
  c3_chart_fn.regions.add = function (regions) {
      var $$ = this.internal, config = $$.config;
      if (!regions) { return config.regions; }
      config.regions = config.regions.concat(regions);
      $$.redrawWithoutRescale();
      return config.regions;
  };
  c3_chart_fn.regions.remove = function (options) {
      var $$ = this.internal, config = $$.config,
          duration, classes, regions;
  
      options = options || {};
      duration = $$.getOption(options, "duration", config.transition_duration);
      classes = $$.getOption(options, "classes", [CLASS.region]);
  
      regions = $$.main.select('.' + CLASS.regions).selectAll(classes.map(function (c) { return '.' + c; }));
      (duration ? regions.transition().duration(duration) : regions)
          .style('opacity', 0)
          .remove();
  
      config.regions = config.regions.filter(function (region) {
          var found = false;
          if (!region['class']) {
              return true;
          }
          region['class'].split(' ').forEach(function (c) {
              if (classes.indexOf(c) >= 0) { found = true; }
          });
          return !found;
      });
  
      return config.regions;
  };
  