The modes available to measure VisualElement sizes.
This enum value is passed to VisualElement.DoMeasure. This lets UI elements indicate their natural size during the layout algorithm.
|Undefined||The element should give its preferred width/height without any constraint.|
|Exactly||The element should give the width/height that is passed in and derive the opposite site from this value (for example, calculate text size from a fixed width).|
|AtMost||At Most. The element should give its preferred width/height but no more than the value passed.|