Set the horizontal alignment within the cell.
Set the vertical alignment within the cell.
Set horizontal and vertical alignment within the cell.
Reserve padding around the child inside its cell.
Make the child cover columns columns and rows rows from its cell.
A placed grid child, returned by Grid.add/Grid.addSizer for fluent configuration:
Every modifier returns the same GridItem, so calls chain. The grid reads the item's final state at layout time, so configuration may continue after add. Alignment uses the same HAlign/VAlign as the box sizers.