code: function changedActiveItems(regionMapping) {
    if (defined(regionMapping._regionDetails)) {
      reviseLegendHelper(regionMapping);
      if (!regionMapping._loadingData) {
        if (
          defined(regionMapping._imageryLayer) ||
          defined(regionMapping._hadImageryAtLayerIndex)
        ) {
          redisplayRegions(regionMapping);
        }
        regionMapping._changed.raiseEvent(regionMapping);
      }
    } else {
      regionMapping._legendHelper = undefined;
      regionMapping._legendUrl = undefined;
    }
  }
docs: Call when the active column changes, or when the table data source is first shown.
  Generates a LegendHelper.
  For lat/lon files, updates entities and extent.
  For region files, rebuilds and redisplays the imageryLayer.
  @private