Direction right? Up or down? I think I'm missing something.
By default the grid's items are added to the right of the previous, in a single line. If the number of specified columns is reached (maxPerLine), a new row is started. If you set the number of columns to '1', it will be going down instead of right.
That's all assuming the direction is set to "horizontal".
If you change the direction to "vertical", it's the same thing, but with Y and X flipped, basically. Instead of extending toward the right, it will extend downward. "maxPerLine" becomes number of rows instead of columns, and if this number is reached, a new column gets started (to the right of the first one).