The way of stacking series being contained in Series Group.
| NONE | "none" | Do not stack. |
| NORMAL | "normal" | Stack items of each series in order from axis. |
| FILL | "fill" | Stack items of each series in order from axis. Display items relatively so that they can fill minimum and maximum value of value axis. |
| OVERLAPPED | "overlapped" | Display items being contained in each series all from axis. Display by stacking. The display order is determined by zindex. |