The cell selection value is an array of strings - each string representing a cell. The string for each cell is the value of the
idProperty for that row, followed by a comma, followed by the name/id of corresponding column:
<idProperty value>,<column id or name>.
Try and select a few cells in the grid above, then sort the grid by the
age column and see selected cells remaining appropriately selected even after the sort. This is because the
idProperty is used in the value for each selected cell.
You can use the little square at the bottom-right border of the active cell to drag and extend the current cell selection.