The OffspringItem control has an Additions property, which is a container control for the Addition controls. This contol implements the IEnumerable<Addition> interface, so it is easy to get the inner Addition controls.

The Additioncontrol can be attached to the item to provide some extra functionality both on server side, as well as on client side. The addition is similiar to the generic ASP.NET extender, but is designed to cooperate with MForm item controls.

Each addition control has a html representation, however this representation is not displayed. This is particularly important for MForm items that are dynamically added on client side. The template node of the MForm item is cloned on the client side along with its html addition representations. When the added item is loaded, also its additions are loaded and the new MForm controls has all its additions working.

A special type of Addition controls are Constraint controls, which take part in items' validation process. Constraint controls are described in the next chapter.