Optional alignmentThe content alignment of the panel.
Possible values are documented in BoxLayout.Alignment.
The default is 'start'.
Optional directionThe layout direction of the panel.
Possible values are documented in BoxLayout.Direction.
The default is 'top-to-bottom'.
Optional layoutThe box layout to use for the box panel.
If this is provided, the other options are ignored.
The default is a new BoxLayout.
Optional spacingThe spacing between items in the panel.
The default is 4.
An options object for initializing a box panel.