Where a UIPanel lines its children up across the layout.
"start": the left of a column, the top of a row, the top left of a grid cell
"center": the middle
"end": the right of a column, the bottom of a row
"stretch": resize each child to the full width of a column, the full
height of a row, or the width of a grid cell. Only a UITextButton
or a UIPanel is resized; any other child keeps its size and lines
up at the start.
Where a UIPanel lines its children up across the layout.
"start": the left of a column, the top of a row, the top left of a grid cell"center": the middle"end": the right of a column, the bottom of a row"stretch": resize each child to the full width of a column, the full height of a row, or the width of a grid cell. Only a UITextButton or a UIPanel is resized; any other child keeps its size and lines up at the start.