The :wrap property is not implemented, and mostly useless: the
FlowLayout is a reflowing grid. This means that if it receives
less than the preferred width or height in the flow direction
then it should always reflow.
FlowLayout is a layout manager that arranges its children in a
reflowing line; the orientation controls the major axis for the
layout: horizontal, for reflow on the Y axis, and vertical, for
reflow on the X axis.
