This type inherits from ItemsChartSettingsItemClass.
Group ID for legend. Items in the same group have a different toggle behavior. When all the items in a group are enabled, clicking an item causes that item to stay enabled and all other items are disabled. Clicking it again enables all items again. Consequently, at least one item in each group is always enabled. The exception to this is if the group ID is null (no group) or the group contains only one item. Then the item is toggled on/off individually.
Name to use in legend
Whether or not to show in legend.