An annotation is a special form of syntactic metadata that can be added to components. The definitions, properties and components themselves may be annotated. The annotations can be retrieved at the run time.
The annotations have no direct effect on the operation of the components. Rather, they are mainly used for UI designers to annotate metadata, such that it controls how a tool or a utility shall do at run-time. The content and meanings of annotations totally depend on the tools or the utilities the developer uses. For example, ZK Bind examines annotations to know how to load and store the value of a component.