Here the schema http://xmlns.oracle.com/weblogic/jdbc-data-source/1.5/jdbc-data-source.xsd
and here the documentation : https://docs.oracle.com/cd/E24329_01/web.1211/e24367/jdbc_multidatasources.htm#JDBCA209
"The name of the application class to handle the callback sent when a multi data source is ready to failover or fail back connection requests to another data source within the multi data source. The name must be the absolute name of an application class that implements the weblogic.jdbc.extensions.ConnectionPoolFailoverCallback interface."
and here the documentation : https://docs.oracle.com/cd/E24329_01/web.1211/e24367/jdbc_multidatasources.htm#JDBCA209
"The name of the application class to handle the callback sent when a multi data source is ready to failover or fail back connection requests to another data source within the multi data source. The name must be the absolute name of an application class that implements the weblogic.jdbc.extensions.ConnectionPoolFailoverCallback interface."