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 separate ORM functionality available from EclipseLink that goes beyond those features made available through JPA.
Some of these features include basic collections and maps, additional caching features, change tracking, converters, and named stored procedure queries.
See Using EclipseLink JPA Extensions (ELUG) and the org.eclipse.persistence.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. Some of these options include customizing the database connection, caching, customizing descriptors, and more.
See How to use the Persistence Unit Properties in the EclipseLink User's Guide and the org.eclipse.persistence.jpa.config.PersistenceUnitProperties class for a full list of properties available for configuration.