code: function decorateBackgroundWithLinearGradient(gc, config) {
      var isTransparent,
          bounds = config.bounds,
          grad = gc.createLinearGradient(bounds.x, bounds.y, bounds.x, bounds.y + bounds.height);
  
      (config.gradientStops || this.gradientStops).forEach(function(stop) {
          isTransparent = isTransparent || regexRGBA.test(stop);
          grad.addColorStop.apply(grad, stop);
      });
  
      if (isTransparent) {
          gc.clearRect(bounds.x, bounds.y, bounds.width, bounds.height);
      }
  
      gc.cache.fillStyle = grad;
      gc.fillRect(bounds.x, bounds.y, bounds.width, bounds.height);
  }
docs: @summary Draw vertical gradient behind group label.
  @desc _Do not call this function directly._
  
  Supply a reference to this function in the options object (first plug-in parameter):
  * {@link GroupedHeader#paintBackground options.paintBackground}
  * One or more elements in a {@link GroupedHeader#groupConfig options.groupConfig} array
  
  For example:
  ```js
  myGrid.installPlugins([
  [groupedHeaderPlugin, { paintBackground: groupedHeaderPlugin.decorateBackgroundWithLinearGradient }]
  ]);
  ```
  
  @this {GroupHeader}
  @param {CanvasRenderingContext2D} gc
  @param {object} config - The `paint` method's `config` object.
  @memberOf groupedHeader