Oracle - Significado de sentencia SRW.USER_EXIT

/* Suppose you have a user exit named STORE to which you want 

** to pass salary values from Report Builder.  To do so, you 

** could write the following formula.  

*/

FUNCTION FOO RETURN BOOLEAN IS

BEGIN

IF :SAL >= 0 THEN

   SRW.REFERENCE(:SAL);

   SRW.USER_EXIT('STORE SAL');

ELSE

   SRW.MESSAGE(100, 'FOUND A NEGATIVE SALARY. CHECK THE

 EMP TABLE.');

END IF;

EXCEPTION

    WHEN SRW.UNKNOWN_USER_EXIT THEN

         SRW.MESSAGE(200, 'STORE USER EXIT WAS UNKNOWN.

                     CHECK IF IT''S LINKED.');

    WHEN SRW.USER_EXIT_FAILURE THEN

         SRW.MESSAGE(200, 'STORE USER EXIT FAILED.

                     CHECK ITS CODE.');

RETURN(TRUE);

END;