Each Migration implementation needs to create a destination object - a subclass of
MigrateDestination (or its subclass
MigrateDestinationEntity) -- representing the Drupal object to be created during migration. Most destination classes accept an options array, containing settings which affect how the destination is constructed.
MigrateDestination classes will also call the handlers (subclasses of
MigrateDestinationHandler) to process destination objects and the fields. See the handlers doc page for more information on the handler classes.