When a program invokes dynamic allocation, it normally does so in behalf of an end user. In a TSO/E environment, the end user is a TSO/E terminal. In a batch environment, the end user is the job. The message that dynamic allocation generates might be useful to the end user, and you can write programs to send the users these messages. Use the S99EIMSG and S99EWTP fields of the request block extension to specify that the system is to issue messages to the end user.
Some installations might need to write special message-sending programs. In this case, use the S99ERMSG field of the request block extension to request that the system return the message block to your program instead of being sent.
When you request the messages to be returned or issued, you can control the severity level of the returned or issued messages through the S99EMGSV field of the request block extension.
If you request that messages be returned, or you want to convert a reason code to a message, link to the IBM-supplied IEFDB476 program (as described in Linking to the IEFDB476 program) after dynamic allocation gives control back to your program.