parentWidthPreservation

Indicates how much the parent should preserve its width when calculating preferredSize. Use this to reduce the strength of rigidity in cases where you want the constraints to have more effect on the parent. For example:

parent.width eq max(chil1.width, child2.width)

max relies on a Weak constraint to avoid getting too large, so the parent's width will remain larger if it uses anything greater to preserve itself.