This interface must be implemented by a presentation-level class. A
presentation-level class represents something that occupies physical
space on the page, such as the content of a panel or a
dialog box.
Each implementation of a Component represents a different Component type,
for example a Grid or a Trade Panel.
A component receives a Frame, on which it can set its content element and attach
event listeners.
Components that can have their state saved should also implement br.component.Serializable.