expand : When set to true, widget expands to fill any space not otherwise used in widget's parent.
fill : Determines whether widget fills any extra space allocated to it by the packer, or keeps its own minimal dimensions: NONE (default), X (fill only horizontally), Y (fill only vertically), or BOTH (fill both horizontally and vertically).
side : Determines which side of the parent widget packs against: TOP (default), BOTTOM, LEFT, or RIGHT.
