Defines enumerated values for selection type. 
Selection type can be one of the following enumerated values: 
| Enumerator | 
|---|
| ST_HORZ_AXIS_ONLY | enables to select a range on horizontal axis, full displayed range on vertical axis  | 
| ST_VERT_AXIS_ONLY | enables to select a range on vertical axis, full displayed range on horizontal axis  | 
| ST_VERT_AND_HORZ_AXES | enables to select a range on horizontal and vertical axes  |