<annotation id="unique identifier">
The <annotation> declaration can appear as a child of most XML Schema declarations.
The <annotation> declaration adds two forms of information to your declarations:
Each <annotation> declaration may contain the elements <appinfo> and <documentation>.
These elements may contain any XML content from any namespace.
Each of these elements may also contain a source attribute.
The source attribute is used to refer to an external file that may be used for application information or documentation information.
Annotations usually include <documentation> declarations to describe the features, or uses, of a particular declaration within the XML Schema.