Margins are periodically used to help with layout. In some cases we have skins where Margins are hard coded. It is also a commonly used property in HTML CSS. Unfortunately, because margins are magic keys/values in the properties map of a node (and specified per-layout manager using static methods) this isn't possible to do from CSS. We should add a margins property and place it in the "Misc" properties of the node so as to not add overhead in the most common case where the node doesn't have any margin. The static methods on layout containers should set the margins on the node so as to be backwards compatible, and stop using the property map (which is probably as much overhead as inflating the Misc properties when needed).