Gets the selection mode of the control.
Possible values are: MULTIPLE_CELLS, MULTIPLE_ROWS, NONE, SINGLE_CELL, and SINGLE_ROW. Changing the value of this property sets the selectedCells property to null.
You must set the allowMultipleSelection property to true to select more than one item in the control at the same time.
Information about the selected cells is written to the selectedCells property.
The default value is SINGLE_ROW.