The default value is an UIKit.UIEdgeInsets whose values are all zero.
Application developers can use this property to modify the rectangle that is used by Auto Layout to control the UIKit.UIView's ultimate alignment.
Auto Layout uses "alignment rectangles" to layout subviews rather than the subviews' UIView.Frame. The UIView.Frame of a UIKit.UIView may include visual elements, such as drop-shadows, that are not symmetrical around the UIKit.UIView's logical center. The "alignment rectangle" for a UIKit.UIView should be related to its logical content.
By default, the "alignment rectangle" of a UIKit.UIView is the UIView.Frame plus the UIView.AlignmentRectInsets. The UIView.AlignmentRectForFrame and UIView.FrameForAlignmentRect methods can be used to fully customize the alignment rectangle.