I meant that data can be entered merely by hitting the Tab button and not using the mouse at all.

If you imagine a 3X3 grid and the focus is on cell(1,2). On the hit of tab the behavior should be as follows

First hit: Focus moves to cell(1,3)

Second hit: Focus moves to cell(2,1)

At this point of time, the first row is saved and the second row is editable

Third hit: Focus moves to cell(2,2) and so on.

If focus is on cell(3,3) on the click of tab a new row should be created and the focus should be on (4,1)

In the entire operation, the mouse is used only once to get the first cell in focus. Data is entered only by using the tab button.