When you receive a message, it is preceded by a message envelope. The message envelope is the header for the message and contains information that includes:

• The addresses of the sender and receiver of the message
• An identifier of the message type
• An offset to the actual message.

Refer to Figure 1 for a pictorial view of the JES XCF mapping structure. Use IXZYIXEN to map the message envelope, and use IXZYIXSE to map a system event message. IXZYIXSE points to either IXZYIXJE (if the message is a JES event) or IXCYGEPL (if the message is a XCF event). These macros, in turn, provide the actual event mapping. Also, refer to Obtaining information about JES members in the XCF group (IXZXIXIF macro) for a discussion of the IXZXIXIF macro and the data it returns.