If the SelectionMode property is set to MultiRow, the navigation behavior does not change, but navigating with the keyboard and mouse while pressing SHIFT (including CTRL+SHIFT) will modify a multi-row selection. Before navigation starts, the control marks the current row as an anchor row. When you navigate while pressing SHIFT, the selection includes all rows between the anchor row and the current row.
Selection Keys
The following selection keys modify multi-row selection:
•SHIFT+DOWN ARROW
•SHIFT+UP ARROW
•SHIFT+PAGE DOWN
•SHIFT+PAGE UP
•CTRL+SHIFT+DOWN ARROW
•CTRL+SHIFT+UP ARROW
•CTRL+SHIFT+PAGE DOWN
•CTRL+SHIFT+PAGE UP
Mouse Selection
If the SelectionMode property is set to MultiRow, clicking a row while pressing CTRL or SHIFT will modify a multi-row selection.
When you click a row while pressing SHIFT, the selection includes all rows between the current row and an anchor row located at the position of the current row before the first click. Subsequent clicks while pressing SHIFT changes the current row, but not the anchor row.
If the CTRL key is pressed when navigating, the arrow keys will navigate to the border cells; for example, if you are in the first row and you press CTRL + DOWN you will navigate to the last row, if the SHIFT key is pressed, all the rows will be selected though.