EclipseLink provides advanced annotations that may be used to configure your persistence unit classes. In some cases, these annotations are to work in concert with existing JPA annotations where as other provide access to seperate ORM functionality available from EclipseLink that goes beyond those features made available through JPA.
Features like basic collections and maps, caching features, change tracking, converters and named stored procedure queries to name a few. See the org.eclipse.persistence.jpa.annotations package for the complete list of supported EclipseLink annotations.
EclipseLink also provides a set of extended properties that allow users to customize their persistence units. Options from database connection details to cahing and descriptor customizers. See the org.eclipse.persistence.jpa.config.PersistenceUnitProperties class for a full list of properties available for configuration.