Contains values that specify how items are resized within a LayoutGroup.
Items are auto-sized according to their contents.
The default sizing behavior (either AutoSize or Stretch), determined by the item's alignment and content and by the item arrangement within a group.
Items are stretched proportionally. You can specify a stretch ratio via the LayoutGroup.StretchRatio attached property.
By default, layout items are resized according to the LayoutGroupBase.HorizontalItemSizeMode and LayoutGroupBase.VerticalItemSizeMode properties of the group where the items reside. The LayoutItem.SizeMode property allows you to specify the size mode for individual LayoutItems, overriding the default size mode imposed by the group's settings.